Fix EffectivelyPrivate ErrorProne findings

Author: marcphilipp

junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/MutableExtensionRegistry.java

@@ -304,7 +304,7 @@ public Optional<Extension> getExtension() {
 			return extension;
 		}
 
-		public Class<?> getTestClass() {
+		private Class<?> getTestClass() {
 			return testClass;
 		}
 

junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/TimeoutInvocationFactory.java

@@ -54,7 +54,7 @@ private ScheduledExecutorService getThreadExecutorForSameThreadInvocation() {
 	@SuppressWarnings({ "deprecation", "try" })
 	private abstract static class ExecutorResource implements Store.CloseableResource, AutoCloseable {
 
-		protected final ScheduledExecutorService executor;
+		private final ScheduledExecutorService executor;
 
 		ExecutorResource(ScheduledExecutorService executor) {
 			this.executor = executor;

junit-jupiter-params/src/main/java/org/junit/jupiter/params/ResolverFacade.java

@@ -601,7 +601,7 @@ boolean isAggregator() {
 					|| isAnnotated(getAnnotatedElement(), AggregateWith.class);
 		}
 
-		protected abstract @Nullable Object resolve(Resolver resolver, ExtensionContext extensionContext,
+		abstract @Nullable Object resolve(Resolver resolver, ExtensionContext extensionContext,
 				EvaluatedArgumentSet arguments, int invocationIndex,
 				Optional<ParameterContext> originalParameterContext);
 	}

junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/EngineTestKit.java

@@ -493,7 +493,7 @@ public EngineExecutionResults execute() {
 
 		private static class DisabledOutputDirectoryProvider implements OutputDirectoryProvider {
 
-			public static final OutputDirectoryProvider INSTANCE = new DisabledOutputDirectoryProvider();
+			private static final OutputDirectoryProvider INSTANCE = new DisabledOutputDirectoryProvider();
 
 			private static final String FAILURE_MESSAGE = "Writing outputs is disabled by default when using EngineTestKit. "
 					+ "To enable, configure a custom OutputDirectoryProvider via EngineTestKit#outputDirectoryProvider.";

junit-vintage-engine/src/main/java/org/junit/vintage/engine/execution/TestRun.java

@@ -269,11 +269,11 @@ Optional<VintageTestDescriptor> getUnambiguously(Description description) {
 			// @formatter:on
 		}
 
-		public void incrementSkippedOrStarted() {
+		private void incrementSkippedOrStarted() {
 			skippedOrStartedCount++;
 		}
 
-		public Optional<VintageTestDescriptor> getNextUnstarted() {
+		private Optional<VintageTestDescriptor> getNextUnstarted() {
 			if (skippedOrStartedCount < descriptors.size()) {
 				return Optional.of(descriptors.get(skippedOrStartedCount));
 			}