Add support for private TempDir fields

Resolves junit-team#2687.

documentation/src/docs/asciidoc/release-notes/release-notes-5.8.0-M2.adoc

@@ -88,12 +88,13 @@ on GitHub.
   temporary directory. To revert to the old behavior of using a single temporary directory
   for the entire test class or method (depending on which level the annotation is used),
   you can set the `junit.jupiter.tempdir.scope` configuration parameter to `per_context`.
+* `@TempDir` cleanup resets readable and executable permissions of the root temporary
+  directory and any contained directories instead of failing to delete them.
+* `@TempDir` fields may now be private.
 * New `named()` static factory method in the `Named` interface that serves as an _alias_
   for `Named.of()`. `named()` is intended to be used via `import static`.
 * New `class` URI scheme for dynamic test sources. This allows tests to be located using
   the information available in a `StackTraceElement`.
-* `@TempDir` cleanup resets readable and executable permissions of the root temporary
-  directory and any contained directories instead of failing to delete them.
 * New `assertThrowsExactly` method which is a more strict version of `assertThrows`
   that allows you to assert that the thrown exception has the exact specified class.
 * New `autoCloseArguments` attribute in `@ParameterizedTest` to close `AutoCloseable`

documentation/src/docs/asciidoc/user-guide/writing-tests.adoc

@@ -2183,9 +2183,9 @@ can improve and eventually <<api-evolution, promote>> this feature.
 
 The built-in `{TempDirectory}` extension is used to create and clean up a temporary
 directory for an individual test or all tests in a test class. It is registered by
-default. To use it, annotate a non-private field of type `java.nio.file.Path` or
-`java.io.File` with `{TempDir}` or add a parameter of type `java.nio.file.Path` or
-`java.io.File` annotated with `@TempDir` to a lifecycle method or test method.
+default. To use it, annotate a field of type `java.nio.file.Path` or `java.io.File` with
+`{TempDir}` or add a parameter of type `java.nio.file.Path` or `java.io.File` annotated
+with `@TempDir` to a lifecycle method or test method.
 
 For example, the following test declares a parameter annotated with `@TempDir` for a
 single test method, creates and writes to a file in the temporary directory, and checks
@@ -2212,7 +2212,7 @@ please note that this option is deprecated and will be removed in a future relea
 
 `@TempDir` is not supported on constructor parameters. If you wish to retain a single
 reference to a temp directory across lifecycle methods and the current test method, please
-use field injection, by annotating a non-private instance field with `@TempDir`.
+use field injection by annotating an instance field with `@TempDir`.
 
 The following example stores a _shared_ temporary directory in a `static` field. This
 allows the same `sharedTempDir` to be used in all lifecycle methods and test methods of

junit-jupiter-api/src/main/java/org/junit/jupiter/api/io/TempDir.java

@@ -26,13 +26,13 @@
 import org.junit.jupiter.api.extension.ParameterResolutionException;
 
 /**
- * {@code @TempDir} can be used to annotate a non-private field in a test class
- * or a parameter in a lifecycle method or test method of type {@link Path} or
+ * {@code @TempDir} can be used to annotate a field in a test class or a
+ * parameter in a lifecycle method or test method of type {@link Path} or
  * {@link File} that should be resolved into a temporary directory.
  *
  * <p>Please note that {@code @TempDir} is not supported on constructor
- * parameters. Please use field injection instead, by annotating a non-private
- * instance field with {@code @TempDir}.
+ * parameters. Please use field injection instead by annotating an instance
+ * field with {@code @TempDir}.
  *
  * <h3>Creation</h3>
  *

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

@@ -14,7 +14,6 @@
 import static java.util.stream.Collectors.joining;
 import static org.junit.jupiter.engine.config.JupiterConfiguration.TEMP_DIR_SCOPE_PROPERTY_NAME;
 import static org.junit.platform.commons.util.AnnotationUtils.findAnnotatedFields;
-import static org.junit.platform.commons.util.ReflectionUtils.isPrivate;
 import static org.junit.platform.commons.util.ReflectionUtils.makeAccessible;
 
 import java.io.File;
@@ -99,7 +98,7 @@ private void injectFields(ExtensionContext context, Object testInstance, Class<?
 			Predicate<Field> predicate) {
 
 		findAnnotatedFields(testClass, TempDir.class, predicate).forEach(field -> {
-			assertValidFieldCandidate(field);
+			assertSupportedType("field", field.getType());
 			try {
 				makeAccessible(field).set(testInstance, getPathOrFile(field, field.getType(), context));
 			}
@@ -109,13 +108,6 @@ private void injectFields(ExtensionContext context, Object testInstance, Class<?
 		});
 	}
 
-	private void assertValidFieldCandidate(Field field) {
-		assertSupportedType("field", field.getType());
-		if (isPrivate(field)) {
-			throw new ExtensionConfigurationException("@TempDir field [" + field + "] must not be private.");
-		}
-	}
-
 	/**
 	 * Determine if the {@link Parameter} in the supplied {@link ParameterContext}
 	 * is annotated with {@link TempDir @TempDir}.

junit-jupiter-engine/src/test/java/org/junit/jupiter/engine/extension/TempDirectoryPerContextTests.java

@@ -292,24 +292,6 @@ void resolvesSeparateTempDirWhenAnnotationIsUsedOnAfterAllMethodParameterOnly()
 	@TestMethodOrder(OrderAnnotation.class)
 	class Failures {
 
-		@Test
-		@DisplayName("when @TempDir is used on private static field")
-		@Order(10)
-		void onlySupportsNonPrivateInstanceFields() {
-			var results = executeTestsForClass(AnnotationOnPrivateStaticFieldTestCase.class);
-
-			assertSingleFailedContainer(results, ExtensionConfigurationException.class, "must not be private");
-		}
-
-		@Test
-		@DisplayName("when @TempDir is used on private instance field")
-		@Order(11)
-		void onlySupportsNonPrivateStaticFields() {
-			var results = executeTestsForClass(AnnotationOnPrivateInstanceFieldTestCase.class);
-
-			assertSingleFailedTest(results, ExtensionConfigurationException.class, "must not be private");
-		}
-
 		@Test
 		@DisplayName("when @TempDir is used on static field of an unsupported type")
 		@Order(20)
@@ -368,6 +350,29 @@ void doesNotSupportTempDirAnnotationOnConstructorParameterWithTestInstancePerCla
 
 	}
 
+	@Nested
+	@DisplayName("supports @TempDir")
+	@TestMethodOrder(OrderAnnotation.class)
+	class PrivateFields {
+
+		@Test
+		@DisplayName("on private static field")
+		@Order(10)
+		void supportsPrivateInstanceFields() {
+			executeTestsForClass(AnnotationOnPrivateStaticFieldTestCase.class).testEvents()//
+					.assertStatistics(stats -> stats.started(1).succeeded(1));
+		}
+
+		@Test
+		@DisplayName("on private instance field")
+		@Order(11)
+		void supportsPrivateStaticFields() {
+			executeTestsForClass(AnnotationOnPrivateInstanceFieldTestCase.class).testEvents()//
+					.assertStatistics(stats -> stats.started(1).succeeded(1));
+		}
+
+	}
+
 	private static void assertSingleFailedContainer(EngineExecutionResults results, Class<? extends Throwable> clazz,
 			String message) {
 
@@ -526,6 +531,7 @@ static class AnnotationOnPrivateInstanceFieldTestCase {
 
 		@Test
 		void test() {
+			assertTrue(Files.exists(tempDir));
 		}
 
 	}
@@ -538,6 +544,7 @@ static class AnnotationOnPrivateStaticFieldTestCase {
 
 		@Test
 		void test() {
+			assertTrue(Files.exists(tempDir));
 		}
 
 	}

junit-jupiter-engine/src/test/java/org/junit/jupiter/engine/extension/TempDirectoryPerDeclarationTests.java

@@ -191,24 +191,6 @@ void canBeUsedViaStaticFieldInsideNestedTestClasses() {
 	@TestMethodOrder(OrderAnnotation.class)
 	class Failures {
 
-		@Test
-		@DisplayName("when @TempDir is used on private static field")
-		@Order(10)
-		void onlySupportsNonPrivateInstanceFields() {
-			var results = executeTestsForClass(AnnotationOnPrivateStaticFieldTestCase.class);
-
-			assertSingleFailedContainer(results, ExtensionConfigurationException.class, "must not be private");
-		}
-
-		@Test
-		@DisplayName("when @TempDir is used on private instance field")
-		@Order(11)
-		void onlySupportsNonPrivateStaticFields() {
-			var results = executeTestsForClass(AnnotationOnPrivateInstanceFieldTestCase.class);
-
-			assertSingleFailedTest(results, ExtensionConfigurationException.class, "must not be private");
-		}
-
 		@Test
 		@DisplayName("when @TempDir is used on static field of an unsupported type")
 		@Order(20)
@@ -267,6 +249,29 @@ void doesNotSupportTempDirAnnotationOnConstructorParameterWithTestInstancePerCla
 
 	}
 
+	@Nested
+	@DisplayName("supports @TempDir")
+	@TestMethodOrder(OrderAnnotation.class)
+	class PrivateFields {
+
+		@Test
+		@DisplayName("on private static field")
+		@Order(10)
+		void supportsPrivateInstanceFields() {
+			executeTestsForClass(AnnotationOnPrivateStaticFieldTestCase.class).testEvents()//
+					.assertStatistics(stats -> stats.started(1).succeeded(1));
+		}
+
+		@Test
+		@DisplayName("on private instance field")
+		@Order(11)
+		void supportsPrivateStaticFields() {
+			executeTestsForClass(AnnotationOnPrivateInstanceFieldTestCase.class).testEvents()//
+					.assertStatistics(stats -> stats.started(1).succeeded(1));
+		}
+
+	}
+
 	private static void assertSingleFailedContainer(EngineExecutionResults results, Class<? extends Throwable> clazz,
 			String message) {
 
@@ -306,6 +311,7 @@ static class AnnotationOnPrivateInstanceFieldTestCase {
 
 		@Test
 		void test() {
+			assertTrue(Files.exists(tempDir));
 		}
 
 	}
@@ -318,6 +324,7 @@ static class AnnotationOnPrivateStaticFieldTestCase {
 
 		@Test
 		void test() {
+			assertTrue(Files.exists(tempDir));
 		}
 
 	}