Introduce overloaded readFieldValue() variants in ReflectionUtils

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

@@ -360,7 +360,7 @@ public static <T> T newInstance(Constructor<T> constructor, Object... args) {
 	}
 
 	/**
-	 * Read the value of a potentially inaccessible field.
+	 * Read the value of a potentially inaccessible or nonexistent field.
 	 *
 	 * <p>If the field does not exist, an exception occurs while reading it, or
 	 * the value of the field is {@code null}, an empty {@link Optional} is
@@ -370,13 +370,55 @@ public static <T> T newInstance(Constructor<T> constructor, Object... args) {
 	 * @param fieldName the name of the field; never {@code null} or empty
 	 * @param instance the instance from where the value is to be read; may
 	 * be {@code null} for a static field
+	 * @see #readFieldValue(Field)
+	 * @see #readFieldValue(Field, Object)
 	 */
 	public static <T> Optional<Object> readFieldValue(Class<T> clazz, String fieldName, T instance) {
 		Preconditions.notNull(clazz, "Class must not be null");
 		Preconditions.notBlank(fieldName, "Field name must not be null or blank");
 
+		Field field = null;
+		try {
+			field = makeAccessible(clazz.getDeclaredField(fieldName));
+		}
+		catch (Throwable t) {
+			BlacklistedExceptions.rethrowIfBlacklisted(t);
+			return Optional.empty();
+		}
+		return readFieldValue(field, instance);
+	}
+
+	/**
+	 * Read the value of a potentially inaccessible static field.
+	 *
+	 * <p>If an exception occurs while reading the field or if the value of the
+	 * field is {@code null}, an empty {@link Optional} is returned.
+	 *
+	 * @param field the field to read; never {@code null}
+	 * @see #readFieldValue(Field, Object)
+	 * @see #readFieldValue(Class, String, Object)
+	 */
+	public static Optional<Object> readFieldValue(Field field) {
+		return readFieldValue(field, null);
+	}
+
+	/**
+	 * Read the value of a potentially inaccessible field.
+	 *
+	 * <p>If an exception occurs while reading the field or if the value of the
+	 * field is {@code null}, an empty {@link Optional} is returned.
+	 *
+	 * @param field the field to read; never {@code null}
+	 * @param instance the instance from which the value is to be read; may
+	 * be {@code null} for a static field
+	 * @see #readFieldValue(Field)
+	 * @see #readFieldValue(Class, String, Object)
+	 */
+	public static <T> Optional<Object> readFieldValue(Field field, T instance) {
+		Preconditions.notNull(field, "Field must not be null");
+
 		try {
-			Field field = makeAccessible(clazz.getDeclaredField(fieldName));
+			makeAccessible(field);
 			return Optional.ofNullable(field.get(instance));
 		}
 		catch (Throwable t) {

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

@@ -34,6 +34,7 @@
 import java.io.IOException;
 import java.io.OutputStream;
 import java.lang.reflect.Constructor;
+import java.lang.reflect.Field;
 import java.lang.reflect.Method;
 import java.lang.reflect.Modifier;
 import java.nio.file.Files;
@@ -162,13 +163,34 @@ void newInstance() {
 	}
 
 	@Test
-	void readFieldValueOfExistingField() {
-		assertThat(readFieldValue(MyClass.class, "value", new MyClass(42))).contains(42);
+	void readFieldValueOfNonexistentStaticField() {
+		assertThat(readFieldValue(MyClass.class, "doesNotExist", null)).isNotPresent();
+		assertThat(readFieldValue(MySubClass.class, "staticField", null)).isNotPresent();
 	}
 
 	@Test
-	void readFieldValueOfMissingField() {
-		assertThat(readFieldValue(MyClass.class, "doesNotExist", new MyClass(42))).isEmpty();
+	void readFieldValueOfNonexistentInstanceField() {
+		assertThat(readFieldValue(MyClass.class, "doesNotExist", new MyClass(42))).isNotPresent();
+		assertThat(readFieldValue(MyClass.class, "doesNotExist", new MySubClass(42))).isNotPresent();
+	}
+
+	@Test
+	void readFieldValueOfExistingStaticField() throws Exception {
+		assertThat(readFieldValue(MyClass.class, "staticField", null)).contains(42);
+
+		Field field = MyClass.class.getDeclaredField("staticField");
+		assertThat(readFieldValue(field)).contains(42);
+		assertThat(readFieldValue(field, null)).contains(42);
+	}
+
+	@Test
+	void readFieldValueOfExistingInstanceField() throws Exception {
+		MyClass instance = new MyClass(42);
+		assertThat(readFieldValue(MyClass.class, "instanceField", instance)).contains(42);
+
+		Field field = MyClass.class.getDeclaredField("instanceField");
+		assertThat(readFieldValue(field, instance)).contains(42);
+		assertThat(readFieldValue(field, null)).isNotPresent();
 	}
 
 	@Test
@@ -1136,10 +1158,19 @@ static class Exploder {
 
 	static class MyClass {
 
-		final int value;
+		static final int staticField = 42;
+
+		final int instanceField;
 
 		MyClass(int value) {
-			this.value = value;
+			this.instanceField = value;
+		}
+	}
+
+	static class MySubClass extends MyClass {
+
+		MySubClass(int value) {
+			super(value);
 		}
 	}