Retain stack frames form JUnit Start

Author: mpkorstanje

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

@@ -101,16 +101,19 @@ public static String readStackTrace(Throwable throwable) {
 	/**
 	 * Prune the stack trace of the supplied {@link Throwable}.
 	 *
-	 * <p>Prune all {@linkplain StackTraceElement stack trace elements} up one
-	 * of the supplied {@code classNames} are pruned. All subsequent elements
-	 * in the stack trace will be retained.
+	 * <p>Prune all {@linkplain StackTraceElement stack trace elements} up to one
+	 * of the supplied {@code classNames}. All subsequent elements in the stack
+	 * trace will be retained.
 	 *
 	 * <p>If the {@code classNames} do not match any of the stacktrace elements
 	 * then the {@code org.junit}, {@code jdk.internal.reflect}, and
 	 * {@code sun.reflect} packages are pruned.
 	 *
-	 * <p>Additionally, all elements prior to and including the first JUnit Platform
-	 * Launcher call will be removed.
+	 * <p>Additionally:
+	 * <ul>
+	 *     <li>all elements prior to and including the first JUnit Platform Launcher call will be removed.
+	 *     <li>all elements prior to and including {@code org.junit.start} are kept.
+	 * </ul>
 	 *
 	 * @param throwable the {@code Throwable} whose stack trace should be pruned;
 	 * never {@code null}
@@ -126,6 +129,7 @@ public static void pruneStackTrace(Throwable throwable, List<String> classNames)
 
 		List<StackTraceElement> stackTrace = Arrays.asList(throwable.getStackTrace());
 		List<StackTraceElement> prunedStackTrace = new ArrayList<>();
+		List<StackTraceElement> junitStartStackTrace = new ArrayList<>(0);
 
 		Collections.reverse(stackTrace);
 
@@ -142,7 +146,9 @@ public static void pruneStackTrace(Throwable throwable, List<String> classNames)
 				break;
 			}
 			else if (className.startsWith(JUNIT_START_PACKAGE_PREFIX)) {
+				junitStartStackTrace.addAll(prunedStackTrace);
 				prunedStackTrace.clear();
+				junitStartStackTrace.add(element);
 			}
 			else if (className.startsWith(JUNIT_PLATFORM_LAUNCHER_PACKAGE_PREFIX)) {
 				prunedStackTrace.clear();
@@ -152,6 +158,11 @@ else if (STACK_TRACE_ELEMENT_FILTER.test(className)) {
 			}
 		}
 
+		if (!junitStartStackTrace.isEmpty()) {
+			junitStartStackTrace.addAll(prunedStackTrace);
+			prunedStackTrace = junitStartStackTrace;
+		}
+
 		Collections.reverse(prunedStackTrace);
 		throwable.setStackTrace(prunedStackTrace.toArray(new StackTraceElement[0]));
 	}

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

@@ -106,22 +106,27 @@ void pruneStackTraceOfEverythingPriorToFirstLauncherCall() {
 	}
 
 	@Test
-	void pruneStackTraceOfJUnitStart() {
-		var testClassName = ExceptionUtilsTests.class.getCanonicalName();
+	void pruneStackTraceRetainsStackFramesFromJUnitStart() {
+		// Non-test class frames from org.junit are filtered.
+		var testClassName = "com.example.project.HelloTest";
+		var testFileName = "HelloTest.java";
 
 		var exception = new JUnitException("expected");
 		var stackTrace = exception.getStackTrace();
-
 		var extendedStacktrace = Arrays.copyOfRange(stackTrace, 0, stackTrace.length + 2);
-		extendedStacktrace[stackTrace.length] = new StackTraceElement("org.junit.start.JUnit", "run", "JUnit.class", 3);
-		extendedStacktrace[stackTrace.length + 1] = new StackTraceElement(testClassName, "main",
-			"ExceptionUtilsTest.class", 5);
+		extendedStacktrace[0] = new StackTraceElement(testClassName, "stringLength", testFileName, 10);
+		extendedStacktrace[stackTrace.length] = new StackTraceElement("org.junit.start.JUnit", "run", "JUnit.java", 3);
+		extendedStacktrace[stackTrace.length + 1] = new StackTraceElement(testClassName, "main", testFileName, 5);
 		exception.setStackTrace(extendedStacktrace);
 
 		pruneStackTrace(exception, List.of(testClassName));
 
 		assertThat(exception.getStackTrace()) //
-				.noneMatch(element -> element.toString().contains(testClassName + ".main(file:5)"));
+				.extracting(StackTraceElement::toString) //
+				.containsExactly( //
+					"com.example.project.HelloTest.stringLength(HelloTest.java:10)", //
+					"org.junit.start.JUnit.run(JUnit.java:3)", //
+					"com.example.project.HelloTest.main(HelloTest.java:5)");
 	}
 
 	@Test