Optimize common cases

Author: marcphilipp

junit-platform-commons/src/main/java/org/junit/platform/commons/util/CollectionUtils.java

@@ -210,6 +210,13 @@ public static Stream<?> toStream(Object object) {
 	 */
 	@API(status = INTERNAL, since = "1.9.2")
 	public static <T> void forEachInReverseOrder(List<T> list, Consumer<? super T> action) {
+		if (list.isEmpty()) {
+			return;
+		}
+		if (list.size() == 1) {
+			action.accept(list.get(0));
+			return;
+		}
 		for (ListIterator<T> iterator = list.listIterator(list.size()); iterator.hasPrevious();) {
 			action.accept(iterator.previous());
 		}

platform-tests/src/test/java/org/junit/platform/commons/util/CollectionUtilsTests.java

@@ -34,8 +34,13 @@
 import org.junit.jupiter.api.DynamicTest;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.TestFactory;
+import org.junit.jupiter.api.extension.ParameterContext;
 import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.converter.ArgumentConversionException;
+import org.junit.jupiter.params.converter.ArgumentConverter;
+import org.junit.jupiter.params.converter.ConvertWith;
 import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.CsvSource;
 import org.junit.jupiter.params.provider.MethodSource;
 import org.junit.jupiter.params.provider.ValueSource;
 import org.junit.platform.commons.PreconditionViolationException;
@@ -277,13 +282,26 @@ private void toStreamWithPrimitiveArray(Object primitiveArray) {
 		}
 	}
 
-	@Test
-	void iteratesListElementsInReverseOrder() {
-		var items = List.of("foo", "bar", "baz");
+	@ParameterizedTest
+	@CsvSource(delimiter = '|', nullValues = "N/A", textBlock = """
+			        foo,bar,baz | baz,bar,foo
+			        foo,bar     | bar,foo
+			        foo         | foo
+			        N/A         | N/A
+			""")
+	void iteratesListElementsInReverseOrder(@ConvertWith(CommaSeparator.class) List<String> input,
+			@ConvertWith(CommaSeparator.class) List<String> expected) {
 		var result = new ArrayList<>();
 
-		CollectionUtils.forEachInReverseOrder(items, result::add);
+		CollectionUtils.forEachInReverseOrder(input, result::add);
 
-		assertThat(result).containsExactly("baz", "bar", "foo");
+		assertEquals(expected, result);
+	}
+
+	private static class CommaSeparator implements ArgumentConverter {
+		@Override
+		public Object convert(Object source, ParameterContext context) throws ArgumentConversionException {
+			return source == null ? List.of() : List.of(((String) source).split(","));
+		}
 	}
 }