diff --git a/CHANGELOG b/CHANGELOG
index a9f4dbc..e7a4579 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -4,7 +4,8 @@ CHANGELOG
 1.2.1
 -----
 
-* Bump kemitix-parent from 5.1.1 to 5.2.0
+* Bump kemitix-parent from 5.1.1 to 5.2.0 (#55)
+* Bump junit from 4.12 to 5.3.1 [#56)
 
 1.2.0
 -----
diff --git a/Jenkinsfile.groovy b/Jenkinsfile.groovy
index 7f0eaa4..0f91efd 100644
--- a/Jenkinsfile.groovy
+++ b/Jenkinsfile.groovy
@@ -1,6 +1,5 @@
 final String publicRepo = 'https://github.com/kemitix/'
 final String mvn = "mvn --batch-mode --update-snapshots --errors"
-final dependenciesSupportJDK = 10
 
 pipeline {
     agent any
@@ -9,12 +8,6 @@ pipeline {
             steps {
                 withMaven(maven: 'maven', jdk: 'JDK 1.8') {
                     sh "${mvn} clean compile checkstyle:checkstyle pmd:pmd test"
-                    // Code Coverage to Codacy
-                    sh "${mvn} jacoco:report com.gavinmogan:codacy-maven-plugin:coverage " +
-                            "-DcoverageReportFile=target/site/jacoco/jacoco.xml " +
-                            "-DprojectToken=`$JENKINS_HOME/codacy/token` " +
-                            "-DapiToken=`$JENKINS_HOME/codacy/apitoken` " +
-                            "-Dcommit=`git rev-parse HEAD`"
                     // Code Coverage to Jenkins
                     jacoco exclusionPattern: '**/*{Test|IT|Main|Application|Immutable}.class'
                     // PMD to Jenkins
@@ -58,19 +51,10 @@ pipeline {
                 }
             }
         }
-        stage('Build Java 9') {
-            when { expression { dependenciesSupportJDK >= 9 } }
+        stage('Build Java 11') {
             steps {
-                withMaven(maven: 'maven', jdk: 'JDK 9') {
-                    sh "${mvn} clean verify -Djava.version=9"
-                }
-            }
-        }
-        stage('Build Java 10') {
-            when { expression { dependenciesSupportJDK >= 10 } }
-            steps {
-                withMaven(maven: 'maven', jdk: 'JDK 10') {
-                    sh "${mvn} clean verify -Djava.version=10"
+                withMaven(maven: 'maven', jdk: 'JDK 11') {
+                    sh "${mvn} clean verify -Djava.version=11"
                 }
             }
         }
diff --git a/pom.xml b/pom.xml
index 8b5b9e0..99e6f4b 100644
--- a/pom.xml
+++ b/pom.xml
@@ -33,13 +33,16 @@
 
     <properties>
         <java.version>1.8</java.version>
-        <junit.version>4.12</junit.version>
+        <junit.version>5.3.1</junit.version>
+        <mockito.version>2.23.0</mockito.version>
         <assertj.version>3.11.1</assertj.version>
         <lombok.version>1.18.2</lombok.version>
         <tiles-maven-plugin.version>2.12</tiles-maven-plugin.version>
         <kemitix-maven-tiles.version>1.2.0</kemitix-maven-tiles.version>
         <digraph-dependency.basePackage>net.kemitix.mon</digraph-dependency.basePackage>
         <kemitix-checkstyle.version>5.0.0</kemitix-checkstyle.version>
+        <pitest-maven-plugin.version>1.4.3</pitest-maven-plugin.version>
+        <pitest-junit5-plugin.version>0.7</pitest-junit5-plugin.version>
     </properties>
 
     <dependencies>
@@ -49,10 +52,21 @@
             <version>${lombok.version}</version>
             <scope>provided</scope>
         </dependency>
+
         <dependency>
-            <groupId>junit</groupId>
-            <artifactId>junit</artifactId>
-            <version>${junit.version}</version>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-api</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-engine</artifactId>
+            <scope>runtime</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.mockito</groupId>
+            <artifactId>mockito-junit-jupiter</artifactId>
+            <version>${mockito.version}</version>
             <scope>test</scope>
         </dependency>
         <dependency>
@@ -63,6 +77,18 @@
         </dependency>
     </dependencies>
 
+    <dependencyManagement>
+        <dependencies>
+            <dependency>
+                <groupId>org.junit</groupId>
+                <artifactId>junit-bom</artifactId>
+                <version>${junit.version}</version>
+                <type>pom</type>
+                <scope>import</scope>
+            </dependency>
+        </dependencies>
+    </dependencyManagement>
+
     <build>
         <plugins>
             <plugin>
@@ -77,6 +103,19 @@
                     </tiles>
                 </configuration>
             </plugin><!-- tiles-maven-plugin -->
+
+            <plugin>
+                <groupId>org.pitest</groupId>
+                <artifactId>pitest-maven</artifactId>
+                <version>${pitest-maven-plugin.version}</version>
+                <dependencies>
+                    <dependency>
+                        <groupId>org.pitest</groupId>
+                        <artifactId>pitest-junit5-plugin</artifactId>
+                        <version>${pitest-junit5-plugin.version}</version>
+                    </dependency>
+                </dependencies>
+            </plugin>
         </plugins>
     </build>
 
diff --git a/src/test/java/net/kemitix/mon/BeanBuilderTest.java b/src/test/java/net/kemitix/mon/BeanBuilderTest.java
index d36c69e..58b326a 100644
--- a/src/test/java/net/kemitix/mon/BeanBuilderTest.java
+++ b/src/test/java/net/kemitix/mon/BeanBuilderTest.java
@@ -5,15 +5,15 @@ import lombok.RequiredArgsConstructor;
 import lombok.Setter;
 import net.kemitix.mon.experimental.BeanBuilder;
 import org.assertj.core.api.WithAssertions;
-import org.junit.Test;
+import org.junit.jupiter.api.Test;
 
 import java.util.function.Consumer;
 import java.util.function.Supplier;
 
-public class BeanBuilderTest implements WithAssertions {
+class BeanBuilderTest implements WithAssertions {
 
     @Test
-    public void canCreateAndSetupObject() {
+    void canCreateAndSetupObject() {
         //given
         final Supplier<DataObject> template = () -> new DataObject("name");
         final Consumer<DataObject> value = data -> data.setValue("value");
diff --git a/src/test/java/net/kemitix/mon/EitherTest.java b/src/test/java/net/kemitix/mon/EitherTest.java
index 7508b39..7fd835f 100644
--- a/src/test/java/net/kemitix/mon/EitherTest.java
+++ b/src/test/java/net/kemitix/mon/EitherTest.java
@@ -2,12 +2,12 @@ package net.kemitix.mon;
 
 import net.kemitix.mon.experimental.either.Either;
 import org.assertj.core.api.WithAssertions;
-import org.junit.Test;
+import org.junit.jupiter.api.Test;
 
-public class EitherTest implements WithAssertions {
+class EitherTest implements WithAssertions {
 
     @Test
-    public void whenLeft_isLeft() {
+    void whenLeft_isLeft() {
         //when
         final Either<Integer, String> either = Either.left(1);
         //then
@@ -15,7 +15,7 @@ public class EitherTest implements WithAssertions {
     }
 
     @Test
-    public void whenLeft_isNotRight() {
+    void whenLeft_isNotRight() {
         //when
         final Either<Integer, String> either = Either.left(1);
         //then
@@ -23,7 +23,7 @@ public class EitherTest implements WithAssertions {
     }
 
     @Test
-    public void whenRight_isNotLeft() {
+    void whenRight_isNotLeft() {
         //when
         final Either<Integer, String> either = Either.right("1");
         //then
@@ -31,7 +31,7 @@ public class EitherTest implements WithAssertions {
     }
 
     @Test
-    public void whenRight_isRight() {
+    void whenRight_isRight() {
         //when
         final Either<Integer, String> either = Either.right("1");
         //then
@@ -39,7 +39,7 @@ public class EitherTest implements WithAssertions {
     }
 
     @Test
-    public void whenLeft_matchLeft() {
+    void whenLeft_matchLeft() {
         //given
         final Either<Integer, String> either = Either.left(1);
         //then
@@ -50,7 +50,7 @@ public class EitherTest implements WithAssertions {
     }
 
     @Test
-    public void whenRight_matchRight() {
+    void whenRight_matchRight() {
         //given
         final Either<Integer, String> either = Either.right("1");
         //then
@@ -61,7 +61,7 @@ public class EitherTest implements WithAssertions {
     }
 
     @Test
-    public void givenLeft_whenMapLeft_thenMap() {
+    void givenLeft_whenMapLeft_thenMap() {
         //given
         final Either<Integer, String> either = Either.left(2);
         //when
@@ -74,7 +74,7 @@ public class EitherTest implements WithAssertions {
     }
 
     @Test
-    public void givenRight_whenMapRight_thenMap() {
+    void givenRight_whenMapRight_thenMap() {
         //given
         final Either<Integer, String> either = Either.right("2");
         //when
@@ -87,7 +87,7 @@ public class EitherTest implements WithAssertions {
     }
 
     @Test
-    public void givenLeft_whenMapRight_thenDoNothing() {
+    void givenLeft_whenMapRight_thenDoNothing() {
         //given
         final Either<Integer, String> either = Either.left(2);
         //when
@@ -100,7 +100,7 @@ public class EitherTest implements WithAssertions {
     }
 
     @Test
-    public void givenRight_whenMapLeft_thenDoNothing() {
+    void givenRight_whenMapLeft_thenDoNothing() {
         //given
         final Either<Integer, String> either = Either.right("2");
         //when
diff --git a/src/test/java/net/kemitix/mon/MaybeMonadTest.java b/src/test/java/net/kemitix/mon/MaybeMonadTest.java
index bbb6618..4611aa3 100644
--- a/src/test/java/net/kemitix/mon/MaybeMonadTest.java
+++ b/src/test/java/net/kemitix/mon/MaybeMonadTest.java
@@ -2,11 +2,11 @@ package net.kemitix.mon;
 
 import net.kemitix.mon.maybe.Maybe;
 import org.assertj.core.api.WithAssertions;
-import org.junit.Test;
+import org.junit.jupiter.api.Test;
 
 import java.util.function.Function;
 
-public class MaybeMonadTest implements WithAssertions {
+class MaybeMonadTest implements WithAssertions {
 
     private final int v = 1;
     private final Function<Integer, Maybe<Integer>> f = i -> m(i * 2);
@@ -17,7 +17,7 @@ public class MaybeMonadTest implements WithAssertions {
     }
 
     @Test
-    public void leftIdentity() {
+    void leftIdentity() {
         assertThat(
                 m(v).flatMap(f)
         ).isEqualTo(
@@ -26,7 +26,7 @@ public class MaybeMonadTest implements WithAssertions {
     }
 
     @Test
-    public void rightIdentity() {
+    void rightIdentity() {
         assertThat(
                 m(v).flatMap(x -> m(x))
         ).isEqualTo(
@@ -35,7 +35,7 @@ public class MaybeMonadTest implements WithAssertions {
     }
 
     @Test
-    public void associativity() {
+    void associativity() {
         assertThat(
                 m(v).flatMap(f).flatMap(g)
         ).isEqualTo(
diff --git a/src/test/java/net/kemitix/mon/MaybeTest.java b/src/test/java/net/kemitix/mon/MaybeTest.java
index af35dca..efc3fa9 100644
--- a/src/test/java/net/kemitix/mon/MaybeTest.java
+++ b/src/test/java/net/kemitix/mon/MaybeTest.java
@@ -2,7 +2,7 @@ package net.kemitix.mon;
 
 import net.kemitix.mon.maybe.Maybe;
 import org.assertj.core.api.WithAssertions;
-import org.junit.Test;
+import org.junit.jupiter.api.Test;
 
 import java.util.Objects;
 import java.util.Optional;
@@ -13,25 +13,25 @@ import java.util.stream.Stream;
 
 import static net.kemitix.mon.maybe.Maybe.*;
 
-public class MaybeTest implements WithAssertions {
+class MaybeTest implements WithAssertions {
 
     private static <T> Predicate<T> eq(final T value) {
         return v -> Objects.equals(value, v);
     }
 
     @Test
-    public void justMustBeNonNull() {
+    void justMustBeNonNull() {
         assertThatNullPointerException().isThrownBy(() -> just(null))
                 .withMessageContaining("value");
     }
 
     @Test
-    public void nothingReusesTheSameInstance() {
+    void nothingReusesTheSameInstance() {
         assertThat(nothing()).isSameAs(nothing());
     }
 
     @Test
-    public void equality() {
+    void equality() {
         assertThat(just(1)).isEqualTo(just(1));
         assertThat(just(1)).isNotEqualTo(just(2));
         assertThat(just(1)).isNotEqualTo(nothing());
@@ -40,19 +40,19 @@ public class MaybeTest implements WithAssertions {
     }
 
     @Test
-    public void maybeAllowsNull() {
+    void maybeAllowsNull() {
         assertThat(just(1)).isEqualTo(maybe(1));
         assertThat(nothing()).isEqualTo(maybe(null));
     }
 
     @Test
-    public void map() {
+    void map() {
         assertThat(just(1).map(v -> v + 1)).isEqualTo(just(2));
         assertThat(nothing().map(v -> v)).isEqualTo(nothing());
     }
 
     @Test
-    public void mapToNull_thenJustNull() {
+    void mapToNull_thenJustNull() {
         //given
         final Maybe<Integer> maybe = just(1);
         //when
@@ -65,7 +65,7 @@ public class MaybeTest implements WithAssertions {
     }
 
     @Test
-    public void optional_mapToNull_thenJustNull() {
+    void optional_mapToNull_thenJustNull() {
         //given
         final Optional<Integer> optional = Optional.ofNullable(1);
         //when
@@ -75,49 +75,49 @@ public class MaybeTest implements WithAssertions {
     }
 
     @Test
-    public void justHashCode() {
+    void justHashCode() {
         assertThat(just(1).hashCode()).isNotEqualTo(just(2).hashCode());
     }
 
     @Test
-    public void nothingHashCode() {
+    void nothingHashCode() {
         assertThat(nothing().hashCode()).isEqualTo(maybe(null).hashCode());
     }
 
     @Test
-    public void orElseGet() {
+    void orElseGet() {
         assertThat(just(1).orElseGet(() -> -1)).isEqualTo(1);
         assertThat(nothing().orElseGet(() -> -1)).isEqualTo(-1);
     }
 
     @Test
-    public void orElse() {
+    void orElse() {
         assertThat(just(1).orElse(-1)).isEqualTo(1);
         assertThat(nothing().orElse(-1)).isEqualTo(-1);
     }
 
     @Test
-    public void filter() {
+    void filter() {
         assertThat(just(1).filter(eq(1))).isEqualTo(just(1));
         assertThat(just(1).filter(eq(0))).isEqualTo(nothing());
         assertThat(nothing().filter(eq(1))).isEqualTo(nothing());
     }
 
     @Test
-    public void toOptional() {
+    void toOptional() {
         assertThat(just(1).toOptional()).isEqualTo(Optional.of(1));
         assertThat(nothing()
                 .toOptional()).isEqualTo(Optional.empty());
     }
 
     @Test
-    public void fromOptional() {
+    void fromOptional() {
         assertThat(Optional.of(1).map(Maybe::just).orElseGet(Maybe::nothing)).isEqualTo(just(1));
         assertThat(Optional.empty().map(Maybe::just).orElseGet(Maybe::nothing)).isEqualTo(nothing());
     }
 
     @Test
-    public void peek() {
+    void peek() {
         final AtomicInteger ref = new AtomicInteger(0);
         assertThat(just(1).peek(x -> ref.incrementAndGet())).isEqualTo(just(1));
         assertThat(ref.get()).isEqualTo(1);
@@ -127,12 +127,12 @@ public class MaybeTest implements WithAssertions {
     }
 
     @Test
-    public void justOrThrowDoesNotThrow() {
+    void justOrThrowDoesNotThrow() {
         assertThatCode(() -> just(1).orElseThrow(IllegalStateException::new)).doesNotThrowAnyException();
     }
 
     @Test
-    public void justOrThrowReturnsValue() {
+    void justOrThrowReturnsValue() {
         //given
         final Maybe<Integer> maybe = just(1);
         //when
@@ -142,13 +142,13 @@ public class MaybeTest implements WithAssertions {
     }
 
     @Test
-    public void nothingOrThrow() {
+    void nothingOrThrow() {
         assertThatThrownBy(() -> nothing().orElseThrow(IllegalStateException::new)).isInstanceOf(
                 IllegalStateException.class);
     }
 
     @Test
-    public void justToStream() {
+    void justToStream() {
         //when
         final Stream<Integer> stream = just(1).stream();
         //then
@@ -156,7 +156,7 @@ public class MaybeTest implements WithAssertions {
     }
 
     @Test
-    public void nothingToStream() {
+    void nothingToStream() {
         //when
         final Stream<Object> stream = nothing().stream();
         //then
@@ -164,7 +164,7 @@ public class MaybeTest implements WithAssertions {
     }
 
     @Test
-    public void justFlatMap() {
+    void justFlatMap() {
         //given
         final Maybe<Integer> just1 = just(1);
         final Maybe<Integer> just2 = just(2);
@@ -178,7 +178,7 @@ public class MaybeTest implements WithAssertions {
     }
 
     @Test
-    public void nothingFlatMap() {
+    void nothingFlatMap() {
         //given
         final Maybe<Integer> nothing1 = nothing();
         final Maybe<Integer> nothing2 = nothing();
@@ -192,7 +192,7 @@ public class MaybeTest implements WithAssertions {
     }
 
     @Test
-    public void justNothingFlatMap() {
+    void justNothingFlatMap() {
         //given
         final Maybe<Integer> just1 = just(1);
         final Maybe<Integer> nothing2 = nothing();
@@ -206,7 +206,7 @@ public class MaybeTest implements WithAssertions {
     }
 
     @Test
-    public void just_ifNothing_isIgnored() {
+    void just_ifNothing_isIgnored() {
         //given
         final Maybe<Integer> just = just(1);
         final AtomicBoolean capture = new AtomicBoolean(false);
@@ -217,7 +217,7 @@ public class MaybeTest implements WithAssertions {
     }
 
     @Test
-    public void nothing_ifNothing_isCalled() {
+    void nothing_ifNothing_isCalled() {
         //given
         final Maybe<Integer> nothing = nothing();
         final AtomicBoolean capture = new AtomicBoolean(false);
@@ -228,7 +228,7 @@ public class MaybeTest implements WithAssertions {
     }
 
     @Test
-    public void just_whenMatch_thenJustTriggers() {
+    void just_whenMatch_thenJustTriggers() {
         //given
         final Maybe<Integer> maybe = just(1);
         //then
@@ -239,7 +239,7 @@ public class MaybeTest implements WithAssertions {
     }
 
     @Test
-    public void nothing_whenMatch_thenNothingTriggers() {
+    void nothing_whenMatch_thenNothingTriggers() {
         //given
         final Maybe<Integer> maybe = nothing();
         final AtomicBoolean flag = new AtomicBoolean(false);
@@ -253,7 +253,7 @@ public class MaybeTest implements WithAssertions {
     }
 
     @Test
-    public void just_isJust_isTrue() {
+    void just_isJust_isTrue() {
         //given
         final Maybe<Integer> maybe = just(1);
         //when
@@ -263,7 +263,7 @@ public class MaybeTest implements WithAssertions {
     }
 
     @Test
-    public void just_isNothing_isFalse() {
+    void just_isNothing_isFalse() {
         //given
         final Maybe<Integer> maybe = just(1);
         //when
@@ -273,7 +273,7 @@ public class MaybeTest implements WithAssertions {
     }
 
     @Test
-    public void nothing_isJust_isFalse() {
+    void nothing_isJust_isFalse() {
         //given
         final Maybe<Object> maybe = nothing();
         //when
@@ -283,7 +283,7 @@ public class MaybeTest implements WithAssertions {
     }
 
     @Test
-    public void nothing_isNothing_isTrue() {
+    void nothing_isNothing_isTrue() {
         //given
         final Maybe<Object> maybe = nothing();
         //when
@@ -293,7 +293,7 @@ public class MaybeTest implements WithAssertions {
     }
 
     @Test
-    public void just_or_ignoreTheAlternative() {
+    void just_or_ignoreTheAlternative() {
         //given
         final Maybe<String> one = Maybe.just("one");
         //when
@@ -303,7 +303,7 @@ public class MaybeTest implements WithAssertions {
     }
 
     @Test
-    public void nothing_or_isTheAlternative() {
+    void nothing_or_isTheAlternative() {
         //given
         final Maybe<String> one = Maybe.nothing();
         //when
diff --git a/src/test/java/net/kemitix/mon/MonTest.java b/src/test/java/net/kemitix/mon/MonTest.java
index e54f9f9..54efb5b 100644
--- a/src/test/java/net/kemitix/mon/MonTest.java
+++ b/src/test/java/net/kemitix/mon/MonTest.java
@@ -1,6 +1,6 @@
 package net.kemitix.mon;
 
-import org.junit.Test;
+import org.junit.jupiter.api.Test;
 
 import java.util.Optional;
 import java.util.function.Function;
@@ -8,10 +8,10 @@ import java.util.function.Function;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatNullPointerException;
 
-public class MonTest {
+class MonTest {
 
     @Test
-    public void canCreateAndMapCanGetValue() {
+    void canCreateAndMapCanGetValue() {
         //when
         final Mon<String> wrap = Mon.of("test");
         //then
@@ -26,7 +26,7 @@ public class MonTest {
     }
 
     @Test
-    public void canMap() {
+    void canMap() {
         //given
         final Mon<String> wrap = Mon.of("test");
         //when
@@ -36,7 +36,7 @@ public class MonTest {
     }
 
     @Test
-    public void canMapInstance() {
+    void canMapInstance() {
         //given
         final Mon<String> wrap = Mon.of("test");
         //when
@@ -46,7 +46,7 @@ public class MonTest {
     }
 
     @Test
-    public void createWithValidatorAndContinuations() {
+    void createWithValidatorAndContinuations() {
         //given
         final Function<String, Optional<Mon<String>>> factory =
                 Mon.factory(
@@ -65,7 +65,7 @@ public class MonTest {
 
     @Test
 
-    public void canCompare() {
+    void canCompare() {
         //given
         final Mon<String> one = Mon.of("test");
         final Mon<String> same = Mon.of("test");
@@ -76,7 +76,7 @@ public class MonTest {
     }
 
     @Test
-    public void canFlatMap() {
+    void canFlatMap() {
         //given
         final Mon<String> wrap = Mon.of("test");
         //when
@@ -88,13 +88,13 @@ public class MonTest {
     }
 
     @Test
-    public void ofRequiresNonNull() {
+    void ofRequiresNonNull() {
         assertThatNullPointerException().isThrownBy(() -> Mon.of(null));
     }
 
     @Test
     @SuppressWarnings("ResultOfMethodCallIgnored")
-    public void factoryRequiresValidator() {
+    void factoryRequiresValidator() {
         assertThatNullPointerException().isThrownBy(
                 () -> Mon.factory(null, Optional::of, Optional::empty))
                 .withMessageContaining("validator");
@@ -102,7 +102,7 @@ public class MonTest {
 
     @Test
     @SuppressWarnings("ResultOfMethodCallIgnored")
-    public void factoryRequiresOnValid() {
+    void factoryRequiresOnValid() {
         assertThatNullPointerException().isThrownBy(
                 () -> Mon.factory(v -> true, null, Optional::empty))
                 .withMessageContaining("onValid");
@@ -110,14 +110,14 @@ public class MonTest {
 
     @Test
     @SuppressWarnings("ResultOfMethodCallIgnored")
-    public void factoryRequiresOnInvalid() {
+    void factoryRequiresOnInvalid() {
         assertThatNullPointerException().isThrownBy(
                 () -> Mon.factory(v -> true, Optional::of, null))
                 .withMessageContaining("onInvalid");
     }
 
     @Test
-    public void factory() {
+    void factory() {
         //given
         final Function<Integer, Optional<?>> evenMonFactory =
                 Mon.factory((Integer v) -> v % 2 == 0, Optional::of, Optional::empty);
@@ -131,7 +131,7 @@ public class MonTest {
     }
 
     @Test
-    public void shouldGetInvalidResultWhenFactoryApplyWithNull() {
+    void shouldGetInvalidResultWhenFactoryApplyWithNull() {
         //given
         final Function<Object, Optional<?>> factory = Mon.factory(v -> true, Optional::of, Optional::empty);
         //when
@@ -141,7 +141,7 @@ public class MonTest {
     }
 
     @Test
-    public void shouldHaveHashCodeBasedOnContent() {
+    void shouldHaveHashCodeBasedOnContent() {
         //given
         final int hashOfOne = Mon.of("one")
                 .hashCode();
@@ -155,7 +155,7 @@ public class MonTest {
     }
 
     @Test
-    public void shouldHaveEquals() {
+    void shouldHaveEquals() {
         //given
         final Mon<String> one = Mon.of("one");
         final Mon<String> two = Mon.of("two");
diff --git a/src/test/java/net/kemitix/mon/OptionalMonadTest.java b/src/test/java/net/kemitix/mon/OptionalMonadTest.java
index 8284a81..959813f 100644
--- a/src/test/java/net/kemitix/mon/OptionalMonadTest.java
+++ b/src/test/java/net/kemitix/mon/OptionalMonadTest.java
@@ -1,12 +1,12 @@
 package net.kemitix.mon;
 
 import org.assertj.core.api.WithAssertions;
-import org.junit.Test;
+import org.junit.jupiter.api.Test;
 
 import java.util.Optional;
 import java.util.function.Function;
 
-public class OptionalMonadTest implements WithAssertions {
+class OptionalMonadTest implements WithAssertions {
 
     private final int v = 1;
     private final Function<Integer, Optional<Integer>> f = i -> o(i * 2);
@@ -17,7 +17,7 @@ public class OptionalMonadTest implements WithAssertions {
     }
 
     @Test
-    public void leftIdentity() {
+    void leftIdentity() {
         assertThat(
                 o(v).flatMap(f)
         ).isEqualTo(
@@ -26,7 +26,7 @@ public class OptionalMonadTest implements WithAssertions {
     }
 
     @Test
-    public void rightIdentity() {
+    void rightIdentity() {
         assertThat(
                 o(v).flatMap(x -> o(x))
         ).isEqualTo(
@@ -35,7 +35,7 @@ public class OptionalMonadTest implements WithAssertions {
     }
 
     @Test
-    public void associativity() {
+    void associativity() {
         assertThat(
                 o(v).flatMap(f).flatMap(g)
         ).isEqualTo(
diff --git a/src/test/java/net/kemitix/mon/ResultMonadTest.java b/src/test/java/net/kemitix/mon/ResultMonadTest.java
index d82bd71..57d5959 100644
--- a/src/test/java/net/kemitix/mon/ResultMonadTest.java
+++ b/src/test/java/net/kemitix/mon/ResultMonadTest.java
@@ -2,11 +2,11 @@ package net.kemitix.mon;
 
 import net.kemitix.mon.result.Result;
 import org.assertj.core.api.WithAssertions;
-import org.junit.Test;
+import org.junit.jupiter.api.Test;
 
 import java.util.function.Function;
 
-public class ResultMonadTest implements WithAssertions {
+class ResultMonadTest implements WithAssertions {
 
     private final int v = 1;
     private final Function<Integer, Result<Integer>> f = i -> r(i * 2);
@@ -17,7 +17,7 @@ public class ResultMonadTest implements WithAssertions {
     }
 
     @Test
-    public void leftIdentity() {
+    void leftIdentity() {
         assertThat(
                 r(v).flatMap(f)
         ).isEqualTo(
@@ -26,7 +26,7 @@ public class ResultMonadTest implements WithAssertions {
     }
 
     @Test
-    public void rightIdentity() {
+    void rightIdentity() {
         assertThat(
                 r(v).flatMap(x -> r(x))
         ).isEqualTo(
@@ -35,7 +35,7 @@ public class ResultMonadTest implements WithAssertions {
     }
 
     @Test
-    public void associativity() {
+    void associativity() {
         assertThat(
                 r(v).flatMap(f).flatMap(g)
         ).isEqualTo(
diff --git a/src/test/java/net/kemitix/mon/ResultTest.java b/src/test/java/net/kemitix/mon/ResultTest.java
index 2754456..d793dd4 100644
--- a/src/test/java/net/kemitix/mon/ResultTest.java
+++ b/src/test/java/net/kemitix/mon/ResultTest.java
@@ -7,7 +7,7 @@ import net.kemitix.mon.result.ErrorResultException;
 import net.kemitix.mon.result.UnexpectedErrorResultException;
 import net.kemitix.mon.result.Result;
 import org.assertj.core.api.WithAssertions;
-import org.junit.Test;
+import org.junit.jupiter.api.Test;
 
 import java.io.IOException;
 import java.util.concurrent.Callable;
@@ -15,10 +15,10 @@ import java.util.concurrent.atomic.AtomicReference;
 
 import static org.assertj.core.api.Assumptions.assumeThat;
 
-public class ResultTest implements WithAssertions {
+class ResultTest implements WithAssertions {
 
     @Test
-    public void equality() {
+    void equality() {
         assertThat(Result.ok(1)).isEqualTo(Result.ok(1));
         assertThat(Result.ok(1)).isNotEqualTo(Result.ok(2));
         final RuntimeException runtimeException = new RuntimeException();
@@ -30,12 +30,12 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void successHashCodesAreUnique() {
+    void successHashCodesAreUnique() {
         assertThat(Result.ok(1).hashCode()).isNotEqualTo(Result.ok(2).hashCode());
     }
 
     @Test
-    public void errorHashCodesAreUnique() {
+    void errorHashCodesAreUnique() {
         // despite having 'equivalent' exceptions, the exceptions are distinct instances, so should be considered unique
         //given
         final RuntimeException exception1 = new RuntimeException("message");
@@ -46,7 +46,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void whenOk_isOkay() {
+    void whenOk_isOkay() {
         //when
         final Result<String> result = Result.ok("good");
         //then
@@ -54,7 +54,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void whenOkay_isNotError() {
+    void whenOkay_isNotError() {
         //when
         final Result<String> result = Result.ok("good");
         //then
@@ -62,7 +62,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void whenOkay_matchSuccess() {
+    void whenOkay_matchSuccess() {
         //given
         final Result<String> result = Result.ok("good");
         //then
@@ -73,7 +73,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void whenError_isError() {
+    void whenError_isError() {
         //when
         final Result<String> result = Result.error(new Exception());
         //then
@@ -81,7 +81,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void whenError_isNotSuccess() {
+    void whenError_isNotSuccess() {
         //when
         final Result<String> result = Result.error(new Exception());
         //then
@@ -89,7 +89,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void whenError_matchError() {
+    void whenError_matchError() {
         //given
         final Result<Object> result = Result.error(new Exception("bad"));
         //then
@@ -100,7 +100,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void okay_whenFlatMapToOkay_isOkay() {
+    void okay_whenFlatMapToOkay_isOkay() {
         //given
         final Result<String> result = Result.ok("good");
         //when
@@ -114,7 +114,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void okay_whenFlatMapToError_isError() {
+    void okay_whenFlatMapToError_isError() {
         //given
         final Result<String> result = Result.ok("good");
         //when
@@ -124,7 +124,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void error_whenFlatMapToOkay_isError() {
+    void error_whenFlatMapToOkay_isError() {
         //given
         final Result<String> result = Result.error(new Exception("bad"));
         //when
@@ -134,7 +134,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void error_whenFlatMapToError_isError() {
+    void error_whenFlatMapToError_isError() {
         //given
         final Result<String> result = Result.error(new Exception("bad"));
         //when
@@ -144,7 +144,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void okay_whenMap_isOkay() {
+    void okay_whenMap_isOkay() {
         //given
         final Result<Integer> okResult = Result.ok(1);
         //when
@@ -158,7 +158,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void error_whenMap_isError() {
+    void error_whenMap_isError() {
         //given
         final RuntimeException exception = new RuntimeException();
         final Result<Integer> errorResult = Result.error(exception);
@@ -173,7 +173,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void okay_whenMaybe_wherePasses_isOkayJust() {
+    void okay_whenMaybe_wherePasses_isOkayJust() {
         //given
         final Result<Integer> okResult = Result.ok(1);
         //when
@@ -187,7 +187,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void okay_whenMaybe_whereFails_isOkayNothing() {
+    void okay_whenMaybe_whereFails_isOkayNothing() {
         //given
         final Result<Integer> okResult = Result.ok(1);
         //when
@@ -201,7 +201,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void error_whenMaybe_wherePasses_isError() {
+    void error_whenMaybe_wherePasses_isError() {
         //given
         final RuntimeException exception = new RuntimeException();
         final Result<Integer> errorResult = Result.error(exception);
@@ -216,7 +216,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void error_whenMaybe_whereFails_isError() {
+    void error_whenMaybe_whereFails_isError() {
         //given
         final RuntimeException exception = new RuntimeException();
         final Result<Integer> errorResult = Result.error(exception);
@@ -231,7 +231,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void just_whenFromMaybe_isOkay() {
+    void just_whenFromMaybe_isOkay() {
         //given
         final Maybe<Integer> just = Maybe.just(1);
         //when
@@ -245,7 +245,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void nothing_whenFromMaybe_isError() {
+    void nothing_whenFromMaybe_isError() {
         //given
         final Maybe<Object> nothing = Maybe.nothing();
         final RuntimeException exception = new RuntimeException();
@@ -260,7 +260,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void okay_whenToMaybe_isJust() {
+    void okay_whenToMaybe_isJust() {
         //given
         final Result<Integer> ok = Result.ok(1);
         //when
@@ -270,7 +270,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void error_whenToMaybe_isNothing() {
+    void error_whenToMaybe_isNothing() {
         //given
         final Result<Object> error = Result.error(new RuntimeException());
         //when
@@ -280,7 +280,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void okay_whenOrElseThrow_isValue() throws Throwable {
+    void okay_whenOrElseThrow_isValue() throws Throwable {
         //given
         final Result<Integer> ok = Result.ok(1);
         //when
@@ -290,7 +290,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void error_whenOrElseThrow_throws() {
+    void error_whenOrElseThrow_throws() {
         //given
         final RuntimeException exception = new RuntimeException();
         final Result<Integer> error = Result.error(exception);
@@ -300,7 +300,8 @@ public class ResultTest implements WithAssertions {
                 .hasCause(exception);
     }
 
-    @Test public void okay_whenOrElseThrowT_isValue() throws Exception {
+    @Test
+    void okay_whenOrElseThrowT_isValue() throws Exception {
         //given
         final Result<Integer> ok = Result.ok(1);
         //when
@@ -309,7 +310,7 @@ public class ResultTest implements WithAssertions {
         assumeThat(value).isEqualTo(1);
     }
 
-    @Test public void errorT_whenOrElseThrowT_throwsT() {
+    @Test void errorT_whenOrElseThrowT_throwsT() {
         //given
         final RuntimeException exception = new RuntimeException();
         final Result<Object> error = Result.error(exception);
@@ -317,7 +318,8 @@ public class ResultTest implements WithAssertions {
         assertThatThrownBy(() -> error.orElseThrow(RuntimeException.class)).isSameAs(exception);
     }
 
-    @Test public void errorR_whenOrElseThrowT_throwsWrappedR() {
+    @Test
+    void errorR_whenOrElseThrowT_throwsWrappedR() {
         //given
         final IOException exception = new IOException();
         final Result<Object> error = Result.error(exception);
@@ -327,7 +329,8 @@ public class ResultTest implements WithAssertions {
                 .hasCause(exception);
     }
 
-    @Test public void okay_whenOrElseThrowUnchecked_isValue() {
+    @Test
+    void okay_whenOrElseThrowUnchecked_isValue() {
         //given
         final Result<Integer> ok = Result.ok(1);
         //when
@@ -336,7 +339,8 @@ public class ResultTest implements WithAssertions {
         assumeThat(value).isEqualTo(1);
     }
 
-    @Test public void error_whenOrElseThrowUnchecked_throwsWrapped() {
+    @Test
+    void error_whenOrElseThrowUnchecked_throwsWrapped() {
         //given
         final IOException exception = new IOException();
         final Result<Object> error = Result.error(exception);
@@ -347,7 +351,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void justOkay_whenInvert_thenOkayJust() {
+    void justOkay_whenInvert_thenOkayJust() {
         //given
         final Maybe<Result<Integer>> justSuccess = Maybe.just(Result.ok(1));
         //when
@@ -360,7 +364,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void JustError_whenInvert_isError() {
+    void JustError_whenInvert_isError() {
         //given
         final RuntimeException exception = new RuntimeException();
         final Maybe<Result<Object>> justError = Maybe.just(Result.error(exception));
@@ -374,7 +378,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void nothing_whenInvert_thenOkayNothing() {
+    void nothing_whenInvert_thenOkayNothing() {
         //given
         final Maybe<Result<Integer>> nothing = Maybe.nothing();
         //when
@@ -387,7 +391,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void useCase_whenOkay_thenReturnSuccess() {
+    void useCase_whenOkay_thenReturnSuccess() {
         //given
         final UseCase useCase = UseCase.isOkay();
         //when
@@ -400,7 +404,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void useCase_whenFirstReadIsError_thenReturnError() {
+    void useCase_whenFirstReadIsError_thenReturnError() {
         //given
         final UseCase useCase = UseCase.firstReadInvalid();
         //when
@@ -415,7 +419,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void useCase_whenSecondReadIsError_thenReturnError() {
+    void useCase_whenSecondReadIsError_thenReturnError() {
         //given
         final UseCase useCase = UseCase.secondReadInvalid();
         //when
@@ -431,7 +435,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void okay_toString() {
+    void okay_toString() {
         //given
         final Result<Integer> ok = Result.ok(1);
         //when
@@ -441,7 +445,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void error_toString() {
+    void error_toString() {
         //given
         final Result<Integer> error = Result.error(new RuntimeException("failed"));
         //when
@@ -451,7 +455,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void value_whenResultOf_isOkay() {
+    void value_whenResultOf_isOkay() {
         //given
         final Callable<String> c = () -> "okay";
         //when
@@ -464,7 +468,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void exception_whenResultOf_isError() {
+    void exception_whenResultOf_isError() {
         //given
         final Callable<String> c = () -> {
             throw new IOException();
@@ -479,7 +483,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void okay_whenPeek_isConsumed() {
+    void okay_whenPeek_isConsumed() {
         //given
         final Result<Integer> result = Result.ok(1);
         final AtomicReference<Integer> consumed = new AtomicReference<>(0);
@@ -491,7 +495,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void error_whenPeek_isNotConsumed() {
+    void error_whenPeek_isNotConsumed() {
         //given
         final Result<Integer> result = Result.error(new RuntimeException());
         final AtomicReference<Integer> consumed = new AtomicReference<>(0);
@@ -503,7 +507,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void okay_whenOnError_isIgnored() {
+    void okay_whenOnError_isIgnored() {
         //given
         final Result<Integer> ok = Result.ok(1);
         //when
@@ -511,7 +515,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void error_whenOnError_isConsumed() {
+    void error_whenOnError_isConsumed() {
         //given
         final RuntimeException exception = new RuntimeException();
         final Result<Integer> error = Result.error(exception);
@@ -523,7 +527,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void okay_whenRecover_thenNoChange() {
+    void okay_whenRecover_thenNoChange() {
         //given
         final Result<Integer> ok = Result.ok(1);
         //when
@@ -533,7 +537,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void error_whenRecover_isSuccess() {
+    void error_whenRecover_isSuccess() {
         //given
         final Result<Integer> error = Result.error(new RuntimeException());
         //when
@@ -543,7 +547,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void error_whenRecover_whereError_isUpdatedError() {
+    void error_whenRecover_whereError_isUpdatedError() {
         //given
         final Result<Integer> error = Result.error(new RuntimeException("original"));
         //when
@@ -553,7 +557,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void okay_whenAndThen_whereSuccess_isUpdatedSuccess() {
+    void okay_whenAndThen_whereSuccess_isUpdatedSuccess() {
         //given
         final Result<Integer> ok = Result.ok(1);
         //when
@@ -564,7 +568,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void okay_whenAndThen_whereError_isError() {
+    void okay_whenAndThen_whereError_isError() {
         //given
         final Result<Integer> ok = Result.ok(1);
         final RuntimeException exception = new RuntimeException();
@@ -578,7 +582,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void error_whereAndThen_whereSuccess_isError() {
+    void error_whereAndThen_whereSuccess_isError() {
         //given
         final RuntimeException exception = new RuntimeException();
         final Result<Object> error = Result.error(exception);
@@ -590,7 +594,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void error_whenAndThen_whereError_isOriginalError() {
+    void error_whenAndThen_whereError_isOriginalError() {
         //given
         final RuntimeException exception1 = new RuntimeException();
         final Result<Object> error = Result.error(exception1);
@@ -604,7 +608,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void okay_whenThenWith_whereOkay_isOriginalSuccess() {
+    void okay_whenThenWith_whereOkay_isOriginalSuccess() {
         //given
         final Result<Integer> ok = Result.ok(1);
         //when
@@ -616,7 +620,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void okay_whenThenWith_whereError_thenError() {
+    void okay_whenThenWith_whereError_thenError() {
         //given
         final Result<Integer> ok = Result.ok(1);
         final RuntimeException exception = new RuntimeException();
@@ -630,7 +634,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void error_whenThenWith_whereOkay_thenOriginalError() {
+    void error_whenThenWith_whereOkay_thenOriginalError() {
         //given
         final RuntimeException exception = new RuntimeException();
         final Result<Integer> error = Result.error(exception);
@@ -643,7 +647,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void error_whenThenWith_whenError_thenOriginalError() {
+    void error_whenThenWith_whenError_thenOriginalError() {
         //given
         final RuntimeException exception = new RuntimeException();
         final Result<Integer> error = Result.error(exception);
@@ -656,7 +660,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void okayJust_whenFlatMapMaybe_whereOkayJust_thenIsOkayJust() {
+    void okayJust_whenFlatMapMaybe_whereOkayJust_thenIsOkayJust() {
         //given
         final Result<Maybe<Integer>> okJust = Result.ok(Maybe.just(1));
         //when
@@ -669,7 +673,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void okayJust_whenFlatMapMaybe_whereOkayNothing_thenIsOkayNothing() {
+    void okayJust_whenFlatMapMaybe_whereOkayNothing_thenIsOkayNothing() {
         //given
         final Result<Maybe<Integer>> okJust = Result.ok(Maybe.just(1));
         //when
@@ -682,7 +686,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void okayJust_whenFlatMapMaybe_whereError_thenIsError() {
+    void okayJust_whenFlatMapMaybe_whereError_thenIsError() {
         //given
         final Result<Maybe<Integer>> okJust = Result.ok(Maybe.just(1));
         final RuntimeException exception = new RuntimeException();
@@ -696,7 +700,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void okayNothing_whenFlatMapMaybe_thenDoNotApply() {
+    void okayNothing_whenFlatMapMaybe_thenDoNotApply() {
         //given
         final Result<Maybe<Integer>> okNothing = Result.ok(Maybe.nothing());
         //when
@@ -709,7 +713,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void error_whenFlatMapMaybe_thenDoNotApply() {
+    void error_whenFlatMapMaybe_thenDoNotApply() {
         //given
         final RuntimeException exception = new RuntimeException();
         final Result<Maybe<Integer>> maybeResult = Result.error(exception);
@@ -723,7 +727,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void okayOkay_whenReduce_thenCombine() {
+    void okayOkay_whenReduce_thenCombine() {
         //given
         final Result<Integer> result1 = Result.ok(1);
         final Result<Integer> result10 = Result.ok(10);
@@ -737,7 +741,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void okayError_whenReduce_thenError() {
+    void okayError_whenReduce_thenError() {
         //given
         final Result<Integer> result1 = Result.ok(1);
         final RuntimeException exception = new RuntimeException();
@@ -752,7 +756,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void errorOkay_whenReduce_thenError() {
+    void errorOkay_whenReduce_thenError() {
         //given
         final RuntimeException exception = new RuntimeException();
         final Result<Integer> result1 = Result.error(exception);
@@ -767,7 +771,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void errorError_whenReduce_thenError() {
+    void errorError_whenReduce_thenError() {
         //given
         final RuntimeException exception1 = new RuntimeException();
         final Result<Integer> result1 = Result.error(exception1);
diff --git a/src/test/java/net/kemitix/mon/TypeAliasMonadTest.java b/src/test/java/net/kemitix/mon/TypeAliasMonadTest.java
index 90c87df..1a665d9 100644
--- a/src/test/java/net/kemitix/mon/TypeAliasMonadTest.java
+++ b/src/test/java/net/kemitix/mon/TypeAliasMonadTest.java
@@ -1,11 +1,11 @@
 package net.kemitix.mon;
 
 import org.assertj.core.api.WithAssertions;
-import org.junit.Test;
+import org.junit.jupiter.api.Test;
 
 import java.util.function.Function;
 
-public class TypeAliasMonadTest implements WithAssertions {
+class TypeAliasMonadTest implements WithAssertions {
 
     private final int v = 1;
     private final Function<Integer, AnAlias<Integer>> f = i -> a(i * 2);
@@ -16,7 +16,7 @@ public class TypeAliasMonadTest implements WithAssertions {
     }
 
     @Test
-    public void leftIdentity() {
+    void leftIdentity() {
         assertThat(
                 a(v).flatMap(f)
         ).isEqualTo(
@@ -25,7 +25,7 @@ public class TypeAliasMonadTest implements WithAssertions {
     }
 
     @Test
-    public void rightIdentity() {
+    void rightIdentity() {
         final AnAlias<Integer> integerAnAlias = a(v).flatMap(x -> a(x));
         assertThat(
                 integerAnAlias
@@ -35,7 +35,7 @@ public class TypeAliasMonadTest implements WithAssertions {
     }
 
     @Test
-    public void associativity() {
+    void associativity() {
         assertThat(
                 a(v).flatMap(f).flatMap(g)
         ).isEqualTo(
diff --git a/src/test/java/net/kemitix/mon/TypeAliasTest.java b/src/test/java/net/kemitix/mon/TypeAliasTest.java
index 10497bf..7c89ad3 100644
--- a/src/test/java/net/kemitix/mon/TypeAliasTest.java
+++ b/src/test/java/net/kemitix/mon/TypeAliasTest.java
@@ -1,7 +1,7 @@
 package net.kemitix.mon;
 
 import org.assertj.core.util.Strings;
-import org.junit.Test;
+import org.junit.jupiter.api.Test;
 
 import java.util.Arrays;
 import java.util.Collections;
@@ -9,10 +9,10 @@ import java.util.List;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
-public class TypeAliasTest {
+class TypeAliasTest {
 
     @Test
-    public void shouldCreateATypeAliasAndGetTheValue() {
+    void shouldCreateATypeAliasAndGetTheValue() {
         //given
         final String value = "value";
         //when
@@ -27,7 +27,7 @@ public class TypeAliasTest {
     }
 
     @Test
-    public void shouldCreateATypeAliasWithNestedGenericTypes() {
+    void shouldCreateATypeAliasWithNestedGenericTypes() {
         //given
         final Iterable<String> iterable = Collections.emptyList();
         //when
@@ -39,7 +39,7 @@ public class TypeAliasTest {
     }
 
     @Test
-    public void shouldCreateATypeAliasSubclassAndGetTheValue() {
+    void shouldCreateATypeAliasSubclassAndGetTheValue() {
         //given
         final String value = "value";
         //when
@@ -49,7 +49,7 @@ public class TypeAliasTest {
     }
 
     @Test
-    public void shouldNotBeEqualWhenValueTypesAreDifferent() {
+    void shouldNotBeEqualWhenValueTypesAreDifferent() {
         //given
         final TypeAlias<String> stringTypeAlias = givenTypeAlias("1");
         final TypeAlias<Integer> integerTypeAlias = new TypeAlias<Integer>(1) {
@@ -59,7 +59,7 @@ public class TypeAliasTest {
     }
 
     @Test
-    public void shouldBeEqualWhenValuesAreTheSame() {
+    void shouldBeEqualWhenValuesAreTheSame() {
         //given
         final String value = "value";
         final AnAlias anAlias1 = AnAlias.of(value);
@@ -69,7 +69,7 @@ public class TypeAliasTest {
     }
 
     @Test
-    public void shouldNotBeEqualWhenValuesAreNotTheSame() {
+    void shouldNotBeEqualWhenValuesAreNotTheSame() {
         //given
         final AnAlias valueA = AnAlias.of("value a");
         final AnAlias valueB = AnAlias.of("value b");
@@ -78,7 +78,7 @@ public class TypeAliasTest {
     }
 
     @Test
-    public void shouldBeEqualToRawValue() {
+    void shouldBeEqualToRawValue() {
         //given
         final String value = "value";
         final AnAlias anAlias = AnAlias.of(value);
@@ -87,7 +87,7 @@ public class TypeAliasTest {
     }
 
     @Test
-    public void shouldHaveHashCodeOfValue() {
+    void shouldHaveHashCodeOfValue() {
         //given
         final String value = "value";
         final AnAlias anAlias = AnAlias.of(value);
@@ -96,7 +96,7 @@ public class TypeAliasTest {
     }
 
     @Test
-    public void shouldHaveSameToStringAsAliasedType() {
+    void shouldHaveSameToStringAsAliasedType() {
         //given
         final List<Integer> value = Arrays.asList(1, 2, 3);
         //when
@@ -107,7 +107,7 @@ public class TypeAliasTest {
     }
 
     @Test
-    public void shouldMapTypeAlias() {
+    void shouldMapTypeAlias() {
         //given
         final AnAlias anAlias = AnAlias.of("text");
         //when
diff --git a/src/test/java/net/kemitix/mon/combinator/AfterTest.java b/src/test/java/net/kemitix/mon/combinator/AfterTest.java
index 8d5a4eb..d7fc24a 100644
--- a/src/test/java/net/kemitix/mon/combinator/AfterTest.java
+++ b/src/test/java/net/kemitix/mon/combinator/AfterTest.java
@@ -1,6 +1,6 @@
 package net.kemitix.mon.combinator;
 
-import org.junit.Test;
+import org.junit.jupiter.api.Test;
 
 import java.util.ArrayList;
 import java.util.List;
@@ -8,10 +8,10 @@ import java.util.function.Function;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
-public class AfterTest {
+class AfterTest {
 
     @Test
-    public void canCreateAfterCombinator() {
+    void canCreateAfterCombinator() {
         //given
         final List<String> events = new ArrayList<>();
         final Function<Integer, Integer> squareDecorated =
diff --git a/src/test/java/net/kemitix/mon/combinator/AroundTest.java b/src/test/java/net/kemitix/mon/combinator/AroundTest.java
index ee94f2b..56d8a1b 100644
--- a/src/test/java/net/kemitix/mon/combinator/AroundTest.java
+++ b/src/test/java/net/kemitix/mon/combinator/AroundTest.java
@@ -1,6 +1,6 @@
 package net.kemitix.mon.combinator;
 
-import org.junit.Test;
+import org.junit.jupiter.api.Test;
 
 import java.util.ArrayList;
 import java.util.List;
@@ -8,10 +8,10 @@ import java.util.function.Function;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
-public class AroundTest {
+class AroundTest {
 
     @Test
-    public void canCreateAnAroundCombinator() {
+    void canCreateAnAroundCombinator() {
         //given
         final List<String> events = new ArrayList<>();
         final Function<Integer, Integer> squareDecorated =
diff --git a/src/test/java/net/kemitix/mon/combinator/BeforeTest.java b/src/test/java/net/kemitix/mon/combinator/BeforeTest.java
index d14d85c..992a18b 100644
--- a/src/test/java/net/kemitix/mon/combinator/BeforeTest.java
+++ b/src/test/java/net/kemitix/mon/combinator/BeforeTest.java
@@ -1,6 +1,6 @@
 package net.kemitix.mon.combinator;
 
-import org.junit.Test;
+import org.junit.jupiter.api.Test;
 
 import java.util.ArrayList;
 import java.util.List;
@@ -8,10 +8,10 @@ import java.util.function.Function;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
-public class BeforeTest {
+class BeforeTest {
 
     @Test
-    public void canCreateBeforeCombinator() {
+    void canCreateBeforeCombinator() {
         //given
         final List<String> events = new ArrayList<>();
         final Function<Integer, Integer> squareDecorated =
diff --git a/src/test/java/net/kemitix/mon/lazy/LazySupplierTest.java b/src/test/java/net/kemitix/mon/lazy/LazySupplierTest.java
index 78d7def..2cb86df 100644
--- a/src/test/java/net/kemitix/mon/lazy/LazySupplierTest.java
+++ b/src/test/java/net/kemitix/mon/lazy/LazySupplierTest.java
@@ -1,9 +1,7 @@
 package net.kemitix.mon.lazy;
 
 import org.assertj.core.api.WithAssertions;
-import org.junit.Rule;
-import org.junit.Test;
-import org.junit.rules.Timeout;
+import org.junit.jupiter.api.Test;
 
 import java.util.UUID;
 import java.util.concurrent.*;
@@ -11,13 +9,10 @@ import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.function.Supplier;
 
-public class LazySupplierTest implements WithAssertions {
-
-    @Rule
-    public final Timeout timeout = Timeout.seconds(1);
+class LazySupplierTest implements WithAssertions {
 
     @Test
-    public void whenCreateLazyThenSupplierIsNotCalled() {
+    void whenCreateLazyThenSupplierIsNotCalled() {
         //given
         final AtomicBoolean supplierCalled = new AtomicBoolean(false);
         final Supplier<UUID> supplier = () -> {
@@ -31,7 +26,7 @@ public class LazySupplierTest implements WithAssertions {
     }
 
     @Test
-    public void whenCreateLazyThenIsEvaluatedIsFalse() {
+    void whenCreateLazyThenIsEvaluatedIsFalse() {
         //given
         final Supplier<UUID> supplier = UUID::randomUUID;
         //when
@@ -41,7 +36,7 @@ public class LazySupplierTest implements WithAssertions {
     }
 
     @Test
-    public void whenValueThenSupplierIsCalled() {
+    void whenValueThenSupplierIsCalled() {
         //given
         final AtomicBoolean supplierCalled = new AtomicBoolean(false);
         final Supplier<UUID> supplier = () -> {
@@ -56,7 +51,7 @@ public class LazySupplierTest implements WithAssertions {
     }
 
     @Test
-    public void whenValueThenValueIsSameAsSupplier() {
+    void whenValueThenValueIsSameAsSupplier() {
         //given
         final UUID uuid = UUID.randomUUID();
         final Supplier<UUID> supplier = () -> uuid;
@@ -68,7 +63,7 @@ public class LazySupplierTest implements WithAssertions {
     }
 
     @Test
-    public void whenValueThenIsEvaluatedIsTrue() {
+    void whenValueThenIsEvaluatedIsTrue() {
         //given
         final Supplier<UUID> supplier = () -> UUID.randomUUID();
         final Lazy<UUID> lazy = Lazy.of(supplier);
@@ -79,7 +74,7 @@ public class LazySupplierTest implements WithAssertions {
     }
 
     @Test
-    public void whenValueCalledTwiceThenSupplierIsNotCalledAgain() {
+    void whenValueCalledTwiceThenSupplierIsNotCalledAgain() {
         //given
         final AtomicInteger supplierCalledCounter = new AtomicInteger(0);
         final Supplier<UUID> supplier = () -> {
@@ -95,7 +90,7 @@ public class LazySupplierTest implements WithAssertions {
     }
 
     @Test
-    public void whenMapLazyThenSupplierNotCalled() {
+    void whenMapLazyThenSupplierNotCalled() {
         //given
         final UUID uuid = UUID.randomUUID();
         final AtomicBoolean supplierCalled = new AtomicBoolean(false);
@@ -111,7 +106,7 @@ public class LazySupplierTest implements WithAssertions {
     }
 
     @Test
-    public void whenMapLazyValueThenSupplierIsCalled() {
+    void whenMapLazyValueThenSupplierIsCalled() {
         //given
         final UUID uuid = UUID.randomUUID();
         final AtomicBoolean supplierCalled = new AtomicBoolean(false);
@@ -128,7 +123,7 @@ public class LazySupplierTest implements WithAssertions {
     }
 
     @Test
-    public void whenMapLazyValueThenValueIsCorrect() {
+    void whenMapLazyValueThenValueIsCorrect() {
         //given
         final UUID uuid = UUID.randomUUID();
         final AtomicBoolean supplierCalled = new AtomicBoolean(false);
@@ -145,7 +140,7 @@ public class LazySupplierTest implements WithAssertions {
     }
 
     @Test
-    public void whenLazyValueCalledOnTwoThreadsThenSupplierIsOnlyCalledOnce() throws ExecutionException, InterruptedException {
+    void whenLazyValueCalledOnTwoThreadsThenSupplierIsOnlyCalledOnce() throws ExecutionException, InterruptedException {
         //given
         final AtomicInteger supplierCalledCounter = new AtomicInteger(0);
         final CountDownLatch latch = new CountDownLatch(1);
@@ -173,4 +168,4 @@ public class LazySupplierTest implements WithAssertions {
         assertThat(supplierCalledCounter).hasValue(1);
     }
 
-}
\ No newline at end of file
+}
diff --git a/src/test/java/net/kemitix/mon/tree/GeneralisedTreeTest.java b/src/test/java/net/kemitix/mon/tree/GeneralisedTreeTest.java
index 5771434..8cbaa35 100644
--- a/src/test/java/net/kemitix/mon/tree/GeneralisedTreeTest.java
+++ b/src/test/java/net/kemitix/mon/tree/GeneralisedTreeTest.java
@@ -1,17 +1,17 @@
 package net.kemitix.mon.tree;
 
 import org.assertj.core.api.WithAssertions;
-import org.junit.Test;
+import org.junit.jupiter.api.Test;
 
 import java.util.UUID;
 
 import static java.util.Arrays.asList;
 import static java.util.Collections.singletonList;
 
-public class GeneralisedTreeTest implements WithAssertions {
+class GeneralisedTreeTest implements WithAssertions {
 
     @Test
-    public void canCreateAnEmptyLeaf() {
+    void canCreateAnEmptyLeaf() {
         //when
         final Tree<String> leaf = Tree.leaf(null);
         //then
@@ -19,7 +19,7 @@ public class GeneralisedTreeTest implements WithAssertions {
     }
 
     @Test
-    public void canCreateANonEmptyLeaf() {
+    void canCreateANonEmptyLeaf() {
         //given
         final String item = "item";
         //when
@@ -29,7 +29,7 @@ public class GeneralisedTreeTest implements WithAssertions {
     }
 
     @Test
-    public void emptyLeafHasCountZero() {
+    void emptyLeafHasCountZero() {
         //given
         final Tree<Object> tree = Tree.leaf(null);
         //when
@@ -39,7 +39,7 @@ public class GeneralisedTreeTest implements WithAssertions {
     }
 
     @Test
-    public void nonEmptyLeafHasCountOne() {
+    void nonEmptyLeafHasCountOne() {
         //given
         final Tree<String> tree = Tree.leaf("value");
         //when
@@ -49,7 +49,7 @@ public class GeneralisedTreeTest implements WithAssertions {
     }
 
     @Test
-    public void canCreateTreeWithSubTrees() {
+    void canCreateTreeWithSubTrees() {
         //given
         final String treeItem = "tree";
         final String leafItem = "leaf";
@@ -60,7 +60,7 @@ public class GeneralisedTreeTest implements WithAssertions {
     }
 
     @Test
-    public void canMapNestedTrees() {
+    void canMapNestedTrees() {
         //given
         final UUID uid1 = UUID.randomUUID();
         final UUID uid2 = UUID.randomUUID();