Migrate TestFailReporter to JUnit 5 TestFailExtension

Extracts the TestFailReporter inner class from FileBufferFunctions
into a standalone TestFailExtension class that implements
JUnit 5's TestWatcher interface.

Updates FileBufferFunctions to use @RegisterExtension with the
new extension.

Updates rules-replacement.md to reflect the migration.

Author: vogella

rules-replacement.md

@@ -0,0 +1,22 @@
+# JUnit 4 to JUnit 5 Migration: Rules and Extensions
+
+The following table summarizes the JUnit 4 constructs and their corresponding JUnit 5 replacements within the Eclipse Platform UI codebase, as identified in issues [#3629](https://github.com/eclipse-platform/eclipse.platform.ui/issues/3629) and [#3639](https://github.com/eclipse-platform/eclipse.platform.ui/issues/3639).
+
+| JUnit 4 Construct | JUnit 5 Replacement | Location / Note |
+| :--- | :--- | :--- |
+| `CloseTestWindowsRule` | `CloseTestWindowsExtension` | `org.eclipse.ui.tests.harness.util` |
+| `PreferenceMementoRule` | `PreferenceMementoExtension` | `org.eclipse.ui.tests.harness.util` |
+| `HeadlessApplicationRule` | `HeadlessApplicationExtension` | `org.eclipse.e4.ui.tests.rules` |
+| `WorkbenchContextRule` | `WorkbenchContextExtension` | `org.eclipse.e4.ui.tests.rules` |
+| `JFaceActionRule` | `JFaceActionExtension` | `org.eclipse.jface.tests.action` |
+| `SwtLeakTestWatcher` | `SwtLeakExtension` | `org.eclipse.ui.tests` |
+| `PerformanceTestCaseJunit4` | `PerformanceTestCaseJunit5` | Provided by `org.eclipse.test.performance` |
+| `UIPerformanceTestRule` | `UIPerformanceTestRule` | Implements `BeforeAllCallback` / `AfterAllCallback` |
+| `BindingTestSetup` | **Missing** | |
+| `TestFailReporter` | `TestFailExtension` | `org.eclipse.core.filebuffers.tests` |
+
+## Key Observations
+
+*   **Dual Support**: `UIPerformanceTestRule` currently implements both JUnit 4 `ExternalResource` and JUnit 5 `BeforeAllCallback`/`AfterAllCallback` interfaces, allowing it to be used in both environments.
+*   **Performance Migration**: Per issue #3639, `PerformanceTestCaseJunit5` is the functional equivalent of `PerformanceTestCaseJunit4`, requiring updates to annotations and extension usage.
+*   **Pending Replacements**: `BindingTestSetup` does not yet have a specialized JUnit 5 extension equivalent in the repository.

tests/org.eclipse.core.filebuffers.tests/src/org/eclipse/core/filebuffers/tests/FileBufferFunctions.java

@@ -28,19 +28,13 @@
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.RegisterExtension;
-import org.junit.jupiter.api.extension.ExtensionContext;
-import org.junit.jupiter.api.extension.TestWatcher;
 
 
 import org.eclipse.core.filesystem.EFS;
 import org.eclipse.core.filesystem.IFileInfo;
 import org.eclipse.core.filesystem.IFileStore;
 
-import org.eclipse.core.runtime.ILog;
 import org.eclipse.core.runtime.IPath;
-import org.eclipse.core.runtime.IStatus;
-import org.eclipse.core.runtime.Platform;
-import org.eclipse.core.runtime.Status;
 
 import org.eclipse.core.resources.IProject;
 
@@ -104,26 +98,7 @@ protected IPath getPath() {
 	}
 
 	@RegisterExtension
-	public TestFailReporter failReporter= new TestFailReporter();
-
-	public static class TestFailReporter implements TestWatcher {
-
-		private static final String BUNDLE_ID= "org.eclipse.core.filebuffers.tests";
-
-		ILog log= ILog.of(Platform.getBundle(BUNDLE_ID));
-
-		@Override
-		public void testFailed(ExtensionContext context, Throwable e) {
-			IStatus status= new Status(IStatus.ERROR, BUNDLE_ID, "FAIL in " + context.getDisplayName(), e);
-			log.log(status);
-		}
-
-		@Override
-		public void testSuccessful(ExtensionContext context) {
-			IStatus status= new Status(IStatus.INFO, BUNDLE_ID, "PASS in " + context.getDisplayName());
-			log.log(status);
-		}
-	}
+	public TestFailExtension failReporter= new TestFailExtension();
 
 	/*
 	 * Tests getLocation.

tests/org.eclipse.core.filebuffers.tests/src/org/eclipse/core/filebuffers/tests/TestFailExtension.java

@@ -0,0 +1,41 @@
+/*******************************************************************************
+ * Copyright (c) 2000, 2015 IBM Corporation and others.
+ *
+ * This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License 2.0
+ * which accompanies this distribution, and is available at
+ * https://www.eclipse.org/legal/epl-2.0/
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *     IBM Corporation - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.core.filebuffers.tests;
+
+import org.junit.jupiter.api.extension.ExtensionContext;
+import org.junit.jupiter.api.extension.TestWatcher;
+
+import org.eclipse.core.runtime.ILog;
+import org.eclipse.core.runtime.IStatus;
+import org.eclipse.core.runtime.Platform;
+import org.eclipse.core.runtime.Status;
+
+public class TestFailExtension implements TestWatcher {
+
+	private static final String BUNDLE_ID= "org.eclipse.core.filebuffers.tests";
+
+	ILog log= ILog.of(Platform.getBundle(BUNDLE_ID));
+
+	@Override
+	public void testFailed(ExtensionContext context, Throwable e) {
+		IStatus status= new Status(IStatus.ERROR, BUNDLE_ID, "FAIL in " + context.getDisplayName(), e);
+		log.log(status);
+	}
+
+	@Override
+	public void testSuccessful(ExtensionContext context) {
+		IStatus status= new Status(IStatus.INFO, BUNDLE_ID, "PASS in " + context.getDisplayName());
+		log.log(status);
+	}
+}