Fix stack overflow error in assertIterableEquals

Prior to this commit an iterable of iterables (here instances
of java.nio.file.Path) passed to method `assertIterableEquals`
in class `Assertions` of the JUnit Jupiter API yielded a
`StackOverflowError`.

This commit prevent the eternal while-loop by leveraging the
`equals()`-implementation of the non-null expected element.

Fixes #2157

junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertIterableEquals.java

@@ -67,6 +67,11 @@ private static void assertIterableEquals(Iterable<?> expected, Iterable<?> actua
 			if (expectedElement == actualElement) {
 				continue;
 			}
+			// Prevent stack overflow error.
+			// See https://github.com/junit-team/junit5/issues/2157 for details.
+			if (expectedElement != null && expectedElement.equals(actualElement)) {
+				continue;
+			}
 
 			indexes.addLast(processed - 1);
 			assertIterableElementsEqual(expectedElement, actualElement, indexes, messageOrSupplier);

junit-jupiter-engine/src/test/java/org/junit/jupiter/api/AssertIterableEqualsAssertionsTests.java

@@ -14,10 +14,12 @@
 import static org.junit.jupiter.api.AssertionTestUtils.assertMessageEquals;
 import static org.junit.jupiter.api.AssertionTestUtils.assertMessageStartsWith;
 import static org.junit.jupiter.api.AssertionTestUtils.expectAssertionFailedError;
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
 import static org.junit.jupiter.api.Assertions.assertIterableEquals;
 import static org.junit.jupiter.api.IterableFactory.listOf;
 import static org.junit.jupiter.api.IterableFactory.setOf;
 
+import java.nio.file.Path;
 import java.util.List;
 import java.util.Set;
 
@@ -439,4 +441,12 @@ void assertIterableEqualsDifferentNestedIterablesAndMessageSupplier() {
 		}
 	}
 
+	@Test
+	// https://github.com/junit-team/junit5/issues/2157
+	void assertIterableEqualsWithListOfPath() {
+		var expected = listOf(Path.of("1"));
+		var actual = listOf(Path.of("1"));
+		assertDoesNotThrow(() -> assertIterableEquals(expected, actual));
+	}
+
 }