diff --git a/builder/src/test/java/net/kemitix/checkstyle/ruleset/builder/CheckstyleWriterTest.java b/builder/src/test/java/net/kemitix/checkstyle/ruleset/builder/CheckstyleWriterTest.java
index fd813d8..9b5afd9 100644
--- a/builder/src/test/java/net/kemitix/checkstyle/ruleset/builder/CheckstyleWriterTest.java
+++ b/builder/src/test/java/net/kemitix/checkstyle/ruleset/builder/CheckstyleWriterTest.java
@@ -1,10 +1,205 @@
-import static org.junit.Assert.*;
+package net.kemitix.checkstyle.ruleset.builder;
+
+import lombok.val;
+import me.andrz.builder.map.MapBuilder;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.rules.ExpectedException;
+import org.mockito.MockitoAnnotations;
+
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.nio.file.StandardOpenOption;
+import java.util.AbstractMap;
+import java.util.List;
+import java.util.Map;
+import java.util.UUID;
+
+import static org.assertj.core.api.Assertions.assertThat;
 
 /**
- * .
+ * Tests for {@link CheckstyleWriter}.
  *
  * @author Paul Campbell (pcampbell@kemitix.net)
  */
 public class CheckstyleWriterTest {
 
+    private static final String TEMPLATE = "C:%s\nTW:%s";
+
+    private CheckstyleWriter checkstyleWriter;
+
+    private OutputProperties outputProperties;
+
+    private TemplateProperties templateProperties;
+
+    private RulesProperties rulesProperties;
+
+    private String ruleName;
+
+    private Map<RuleLevel, String> outputFiles;
+
+    private Path outputDirectory;
+
+    private Path checkstyleTemplate;
+
+    @org.junit.Rule
+    public ExpectedException exception = ExpectedException.none();
+
+    @Before
+    public void setUp() throws Exception {
+        MockitoAnnotations.initMocks(this);
+        ruleName = UUID.randomUUID()
+                       .toString();
+        outputProperties = new OutputProperties();
+        outputFiles = new MapBuilder<RuleLevel, String>().put(getOutputFile(RuleLevel.LAYOUT))
+                                                         .put(getOutputFile(RuleLevel.NAMING))
+                                                         .put(getOutputFile(RuleLevel.JAVADOC))
+                                                         .put(getOutputFile(RuleLevel.TWEAKS))
+                                                         .put(getOutputFile(RuleLevel.COMPLEXITY))
+                                                         .build();
+        outputProperties.setRulesetFiles(outputFiles);
+        outputDirectory = Files.createTempDirectory("test");
+        outputProperties.setDirectory(outputDirectory);
+        templateProperties = new TemplateProperties();
+        checkstyleTemplate = Files.createTempFile("checkstyle-template", ".xml");
+        Files.write(
+                checkstyleTemplate, TEMPLATE.getBytes(StandardCharsets.UTF_8), StandardOpenOption.TRUNCATE_EXISTING);
+        templateProperties.setCheckstyleXml(checkstyleTemplate);
+        rulesProperties = new RulesProperties();
+        checkstyleWriter = new CheckstyleWriter(outputProperties, templateProperties, rulesProperties);
+    }
+
+    // write rule that matches current level
+    @Test
+    public void writeRuleThatMatchesCurrentLevel() throws Exception {
+        //given
+        val rule = enabledRule(RuleLevel.LAYOUT, RuleParent.TREEWALKER);
+        rulesProperties.getRules()
+                       .add(rule);
+        //when
+        checkstyleWriter.run();
+        //then
+        final List<String> lines = loadOutputFile(RuleLevel.LAYOUT);
+        assertThat(lines).containsExactly("C:", String.format("TW:<module name=\"%s\"/>", ruleName));
+    }
+
+    // write rule that is below current level
+    @Test
+    public void writeRuleThatIsBelowCurrentLevel() throws Exception {
+        //given
+        val rule = enabledRule(RuleLevel.LAYOUT, RuleParent.TREEWALKER);
+        rulesProperties.getRules()
+                       .add(rule);
+        //when
+        checkstyleWriter.run();
+        //then
+        final List<String> lines = loadOutputFile(RuleLevel.NAMING);
+        assertThat(lines).containsExactly("C:", String.format("TW:<module name=\"%s\"/>", ruleName));
+    }
+
+    // write rule with checker parent
+    @Test
+    public void writeRuleWithCheckerParent() throws Exception {
+        //given
+        val rule = enabledRule(RuleLevel.LAYOUT, RuleParent.CHECKER);
+        rulesProperties.getRules()
+                       .add(rule);
+        //when
+        checkstyleWriter.run();
+        //then
+        final List<String> lines = loadOutputFile(RuleLevel.LAYOUT);
+        assertThat(lines).containsExactly(String.format("C:<module name=\"%s\"/>", ruleName), "TW:");
+    }
+
+    // write rule with properties
+    @Test
+    public void writeRuleWithProperties() throws Exception {
+        //given
+        val rule = enabledRule(RuleLevel.LAYOUT, RuleParent.TREEWALKER);
+        rule.getProperties()
+            .put("key", "value");
+        rulesProperties.getRules()
+                       .add(rule);
+        //when
+        checkstyleWriter.run();
+        //then
+        final List<String> lines = loadOutputFile(RuleLevel.LAYOUT);
+        assertThat(lines).containsExactly("C:", String.format("TW:<module name=\"%s\">", ruleName),
+                                          "    <property name=\"key\" value=\"value\"/>", "</module>"
+                                         );
+    }
+
+    // ignore rule that is above current level
+    @Test
+    public void ignoreRuleThatIsAboveCurrentLevel() throws Exception {
+        //given
+        val rule = enabledRule(RuleLevel.NAMING, RuleParent.TREEWALKER);
+        rulesProperties.getRules()
+                       .add(rule);
+        //when
+        checkstyleWriter.run();
+        //then
+        final List<String> lines = loadOutputFile(RuleLevel.LAYOUT);
+        assertThat(lines).containsExactly("C:", "TW:");
+    }
+
+    // ignore rule that has unspecified level
+    @Test
+    public void ignoreRuleThatHasUnspecifiedLevel() throws Exception {
+        //given
+        val rule = enabledRule(RuleLevel.UNSPECIFIED, RuleParent.TREEWALKER);
+        rulesProperties.getRules()
+                       .add(rule);
+        //when
+        checkstyleWriter.run();
+        //then
+        final List<String> lines = loadOutputFile(RuleLevel.LAYOUT);
+        assertThat(lines).containsExactly("C:", "TW:");
+    }
+
+    // throw RTE if template not found
+    @Test
+    public void throwRteIfTemplateNotFound() throws Exception {
+        //given
+        templateProperties.setCheckstyleXml(Paths.get("garbage"));
+        exception.expect(RuntimeException.class);
+        exception.expectMessage("Missing template: garbage");
+        //when
+        checkstyleWriter.run();
+    }
+
+    // throw RTE if error writing file
+    @Test
+    public void throwRteIfErrorWritingFile() throws Exception {
+        //given
+        outputProperties.setDirectory(Paths.get("/../imaginary"));
+        exception.expect(RuntimeException.class);
+        exception.expectMessage("java.nio.file.NoSuchFileException: /../imaginary/checkstyle-LAYOUT.xml");
+        //when
+        checkstyleWriter.run();
+    }
+
+    private Map.Entry<RuleLevel, String> getOutputFile(final RuleLevel level) throws IOException {
+        final String xmlFile = String.format("checkstyle-%s.xml", level.toString());
+        return new AbstractMap.SimpleImmutableEntry<>(level, xmlFile);
+    }
+
+    private List<String> loadOutputFile(final RuleLevel level) throws IOException {
+        final Path file = outputDirectory.resolve(outputFiles.get(level));
+        assertThat(file).as("Output file exists")
+                        .exists();
+        return Files.readAllLines(file, StandardCharsets.UTF_8);
+    }
+
+    private Rule enabledRule(final RuleLevel level, final RuleParent parent) {
+        val rule = new Rule();
+        rule.setName(ruleName);
+        rule.setEnabled(true);
+        rule.setLevel(level);
+        rule.setParent(parent);
+        return rule;
+    }
 }