Adding diffPrinter class

1. Add diffPrinter class
2. replace diff in consoleTestExecutor with diffPrinter - will be deleted evetually
3. mark the location of adding diff in flatPrinter and verboseTreePrinter.

Issue: junit-team#3139

junit-platform-console/src/main/java/org/junit/platform/console/tasks/ConsoleTestExecutor.java

@@ -16,15 +16,11 @@
 import java.net.URL;
 import java.net.URLClassLoader;
 import java.nio.file.Path;
-import java.util.Arrays;
 import java.util.EnumSet;
 import java.util.List;
 import java.util.Optional;
 import java.util.function.Supplier;
 
-import com.github.difflib.text.DiffRow;
-import com.github.difflib.text.DiffRowGenerator;
-
 import org.apiguardian.api.API;
 import org.junit.platform.commons.JUnitException;
 import org.junit.platform.commons.util.ClassLoaderUtils;
@@ -103,10 +99,8 @@ private static void printFoundTestsSummary(PrintWriter out, TestPlan testPlan) {
 	private TestExecutionSummary executeTests(PrintWriter out, Optional<Path> reportsDir) {
 		Launcher launcher = launcherSupplier.get();
 		SummaryGeneratingListener summaryListener = registerListeners(out, reportsDir, launcher);
-
 		LauncherDiscoveryRequest discoveryRequest = new DiscoveryRequestCreator().toDiscoveryRequest(discoveryOptions);
 		launcher.execute(discoveryRequest);
-
 		TestExecutionSummary summary = summaryListener.getSummary();
 		if (summary.getTotalFailureCount() > 0 || outputOptions.getDetails() != Details.NONE) {
 			printSummary(summary, out);
@@ -195,17 +189,8 @@ private void printSummary(TestExecutionSummary summary, PrintWriter out) {
 					ValueWrapper actual = assertionFailedError.getActual();
 					//apply diff function
 					if (isCharSequence(expected) && isCharSequence(actual)) {
-						DiffRowGenerator generator = DiffRowGenerator.create().showInlineDiffs(true).inlineDiffByWord(
-							true).oldTag(f -> "~").newTag(f -> "**").build();
-						List<DiffRow> rows = generator.generateDiffRows(
-							Arrays.asList(expected.getStringRepresentation()),
-							Arrays.asList(actual.getStringRepresentation()));
-
-						out.printf(
-							"\nPlease put the diff result below into a online markdown editor to see markdown effect: \n");
-						for (DiffRow row : rows) {
-							out.printf(" | %s | %s | \n", row.getOldLine(), row.getNewLine());
-						}
+						DiffPrinter.printDiff(out, expected.getStringRepresentation(),
+							actual.getStringRepresentation());
 					}
 
 				}

junit-platform-console/src/main/java/org/junit/platform/console/tasks/DiffPrinter.java

@@ -0,0 +1,34 @@
+/*
+ * Copyright 2015-2024 the original author or authors.
+ *
+ * All rights reserved. This program and the accompanying materials are
+ * made available under the terms of the Eclipse Public License v2.0 which
+ * accompanies this distribution and is available at
+ *
+ * https://www.eclipse.org/legal/epl-v20.html
+ */
+
+package org.junit.platform.console.tasks;
+
+import java.io.PrintWriter;
+import java.util.Arrays;
+import java.util.List;
+
+import com.github.difflib.text.DiffRow;
+import com.github.difflib.text.DiffRowGenerator;
+
+/**
+ * class provide access to printDiff function
+ */
+class DiffPrinter {
+	//print the difference of two print to out
+	static void printDiff(PrintWriter out, String expected, String actual) {
+		DiffRowGenerator generator = DiffRowGenerator.create().showInlineDiffs(true).inlineDiffByWord(true).oldTag(
+			f -> "~").newTag(f -> "**").build();
+		List<DiffRow> rows = generator.generateDiffRows(Arrays.asList(expected), Arrays.asList(actual));
+		out.printf("\nPlease put the diff result below into a online markdown editor to see markdown effect: \n");
+		for (DiffRow row : rows) {
+			out.printf(" | %s | %s | \n", row.getOldLine(), row.getNewLine());
+		}
+	}
+}

junit-platform-console/src/main/java/org/junit/platform/console/tasks/FlatPrintingListener.java

@@ -79,6 +79,7 @@ private void printlnTestDescriptor(Style style, String message, TestIdentifier t
 
 	private void printlnException(Style style, Throwable throwable) {
 		printlnMessage(style, "Exception", ExceptionUtils.readStackTrace(throwable));
+		//add diff here
 	}
 
 	private void printlnMessage(Style style, String message, String detail) {

junit-platform-console/src/main/java/org/junit/platform/console/tasks/VerboseTreePrintingListener.java

@@ -97,6 +97,7 @@ public void executionStarted(TestIdentifier testIdentifier) {
 	@Override
 	public void executionFinished(TestIdentifier testIdentifier, TestExecutionResult testExecutionResult) {
 		testExecutionResult.getThrowable().ifPresent(t -> printDetail(Style.FAILED, "caught", readStackTrace(t)));
+		//add diff here
 		if (testIdentifier.isContainer()) {
 			Long creationMillis = frames.pop();
 			printVerticals(theme.end());