Change Namespace equality to consider parts order.

Not taking into account the order of parts made namespace behavior
non-intuitive.

Closes: junit-team#646

documentation/src/docs/asciidoc/release-notes-5.0.0-M4.adoc

@@ -34,6 +34,8 @@ on GitHub.
 * `--hide-details` option of the `ConsoleLauncher` is deprecated, use `--details none` instead.
 * The ZIP distribution containing the console launcher is no longer provided. It is replaced
   by an executable standalone JAR distribution. For details, see "New Features" section below.
+* ExtensionContext composite Namespaces with the same parts but in different order will
+  not be considered equal.
 
 ===== New Features
 

junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ExtensionContext.java

@@ -14,9 +14,10 @@
 
 import java.lang.reflect.AnnotatedElement;
 import java.lang.reflect.Method;
+import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
-import java.util.HashSet;
+import java.util.List;
 import java.util.Map;
 import java.util.Optional;
 import java.util.Set;
@@ -307,9 +308,9 @@ class Namespace {
 
 		/**
 		 * Create a namespace which restricts access to data to all extensions
-		 * which use the same {@code parts} for creating a namespace.
+		 * which use the same sequence of {@code parts} for creating a namespace.
 		 *
-		 * <p>The order of the {@code parts} is not significant.
+		 * <p>The order of the {@code parts} is significant.
 		 *
 		 * <p>Internally the {@code parts} are compared using {@link Object#equals(Object)}.
 		 */
@@ -319,10 +320,10 @@ public static Namespace create(Object... parts) {
 			return new Namespace(parts);
 		}
 
-		private final Set<?> parts;
+		private final List<?> parts;
 
 		private Namespace(Object... parts) {
-			this.parts = new HashSet<>(Arrays.asList(parts));
+			this.parts = new ArrayList<>(Arrays.asList(parts));
 		}
 
 		@Override

junit-jupiter-engine/src/test/java/org/junit/jupiter/engine/execution/ExtensionValuesStoreTests.java

@@ -11,6 +11,7 @@
 package org.junit.jupiter.engine.execution;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotEquals;
 import static org.junit.jupiter.api.Assertions.assertNull;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 
@@ -312,6 +313,22 @@ void valueFromParentCanBeOverriddenInChild() {
 	@Nested
 	class CompositeNamespaceTests {
 
+		@Test
+		void namespacesEqualForSamePartsSequence() {
+			Namespace ns1 = Namespace.create("part1", "part2");
+			Namespace ns2 = Namespace.create("part1", "part2");
+
+			assertEquals(ns1, ns2);
+		}
+
+		@Test
+		void orderOfNamespacePartsDoesMatter() {
+			Namespace ns1 = Namespace.create("part1", "part2");
+			Namespace ns2 = Namespace.create("part2", "part1");
+
+			assertNotEquals(ns1, ns2);
+		}
+
 		@Test
 		void additionNamespacePartMakesADifferenc() {
 
@@ -329,18 +346,6 @@ void additionNamespacePartMakesADifferenc() {
 			assertEquals(value2, store.get(ns2, key));
 		}
 
-		@Test
-		void orderOfNamespacePartsDoesNotMatter() {
-
-			Namespace ns1 = Namespace.create("part1", "part2");
-			Namespace ns2 = Namespace.create("part2", "part1");
-
-			parentStore.put(ns1, key, value);
-
-			assertEquals(value, store.get(ns1, key));
-			assertEquals(value, store.get(ns2, key));
-		}
-
 	}
 
 	private Object createObject(final String display) {