Improve error message for assertArrayEquals() when multi-dimensional arrays

have different lengths.

Previously, JUnit's assertion error message would indicate only that some array
lengths x and y were unequal, without indicating whether this pertained to the
outer array or some nested array. Now, in case of a length mismatch between two
nested arrays, Junit will tell at which indices they reside.

Closes #1054
Closes #803

Author: Stephan202

src/main/java/org/junit/internal/ComparisonCriteria.java

@@ -25,6 +25,11 @@ public abstract class ComparisonCriteria {
      */
     public void arrayEquals(String message, Object expecteds, Object actuals)
             throws ArrayComparisonFailure {
+        arrayEquals(message, expecteds, actuals, true);
+    }
+
+    private void arrayEquals(String message, Object expecteds, Object actuals, boolean outer)
+            throws ArrayComparisonFailure {
         if (expecteds == actuals
             || Arrays.deepEquals(new Object[] {expecteds}, new Object[] {actuals})) {
             // The reflection-based loop below is potentially very slow, especially for primitive
@@ -34,19 +39,23 @@ public void arrayEquals(String message, Object expecteds, Object actuals)
         }
         String header = message == null ? "" : message + ": ";
 
-        int expectedsLength = assertArraysAreSameLength(expecteds,
-                actuals, header);
+        // Only include the user-provided message in the outer exception.
+        String exceptionMessage = outer ? header : "";
+        int expectedsLength = assertArraysAreSameLength(expecteds, actuals, exceptionMessage);
 
         for (int i = 0; i < expectedsLength; i++) {
             Object expected = Array.get(expecteds, i);
             Object actual = Array.get(actuals, i);
 
             if (isArray(expected) && isArray(actual)) {
                 try {
-                    arrayEquals(message, expected, actual);
+                    arrayEquals(message, expected, actual, false);
                 } catch (ArrayComparisonFailure e) {
                     e.addDimension(i);
                     throw e;
+                } catch (AssertionError e) {
+                    // Array lengths differed.
+                    throw new ArrayComparisonFailure(header, e, i);
                 }
             } else {
                 try {

src/test/java/org/junit/tests/assertion/AssertionTest.java

@@ -211,6 +211,30 @@ public void multiDimensionalArraysAreNotEqualNoMessage() {
         }
     }
 
+    @Test
+    public void multiDimensionalArraysDifferentLengthMessage() {
+        try {
+            assertArrayEquals("message", new Object[][]{{true, true}, {false, false}}, new Object[][]{{true, true}, {false}});
+        } catch (AssertionError exception) {
+            assertEquals("message: arrays first differed at element [1]; array lengths differed, expected.length=2 actual.length=1", exception.getMessage());
+            return;
+        }
+
+        fail("Expected AssertionError to be thrown");
+    }
+
+    @Test
+    public void multiDimensionalArraysDifferentLengthNoMessage() {
+        try {
+            assertArrayEquals(new Object[][]{{true, true}, {false, false}}, new Object[][]{{true, true}, {false}});
+        } catch (AssertionError exception) {
+            assertEquals("arrays first differed at element [1]; array lengths differed, expected.length=2 actual.length=1", exception.getMessage());
+            return;
+        }
+
+        fail("Expected AssertionError to be thrown");
+    }
+
     @Test
     public void arraysWithNullElementEqual() {
         Object[] objects1 = new Object[]{null};