BoxFitterTest: put existing tests inside a nest

src/test/java/net/kemitix/text/fit/BoxFitterTest.java

@@ -2,6 +2,7 @@ package net.kemitix.text.fit;
 
 import org.assertj.core.api.WithAssertions;
 import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Nested;
 import org.junit.jupiter.api.Test;
 
 import java.awt.*;
@@ -22,20 +23,25 @@ public class BoxFitterTest
         implements WithAssertions {
 
     private final BoxFitter boxFitter = TextFit.fitter();
-    private final int imageSize = 300;
-    private final int fontSize = 20;
-    private final Graphics2D graphics2D = graphics(imageSize, imageSize);
     private final Font font;
     private Function<Integer, Font> fontFactory;
-    private Rectangle2D box = new Rectangle(imageSize, imageSize);
 
     public BoxFitterTest() throws URISyntaxException, IOException, FontFormatException {
         URL resource = this.getClass().getResource("alice/Alice-Regular.ttf");
+        int initialFontSize = 20;
         font = Font.createFont(Font.TRUETYPE_FONT, new File(resource.toURI()))
-                .deriveFont(Font.PLAIN, fontSize);
+                .deriveFont(Font.PLAIN, initialFontSize);
         fontFactory = size -> font.deriveFont(Font.PLAIN, size);
     }
 
+    @Nested
+    @DisplayName("Single Box")
+    public class SingleBox {
+
+        private final int imageSize = 300;
+        private final Graphics2D graphics2D = graphics(imageSize, imageSize);
+        private Rectangle2D box = new Rectangle(imageSize, imageSize);
+
         @Test
         @DisplayName("Fit single words")
         public void fitSingleWord() {
@@ -93,6 +99,7 @@ public class BoxFitterTest
         private int invoke(String longText) {
             return boxFitter.fit(longText, fontFactory, graphics2D, box);
         }
+    }
 
     private String longStringGenerator(int cycles) {
         String text = "This is a long piece of text that should result in an " +