Support automatic constructor injection in JUnit Jupiter

Prior to this commit, dependency injection of all arguments in a test
class constructor invoked by JUnit Jupiter was only possible if the
constructor was explicitly annotated with @Autowired.

This commit introduces support for a configurable "test constructor
autowire" mode which defaults to false in order to remain backwards
compatible.

Specifically, this mode can be configured globally for an entire test
suite via a new "spring.test.constructor.autowire" JVM system property
that can alternatively be configured via the SpringProperties
mechanism. In addition, the global "test constructor autowire" mode can
be overridden locally on a per-class basis via the new @TestConstructor
annotation.

Closes gh-22286

spring-test/src/test/java/org/springframework/test/context/junit/jupiter/TestConstructorAnnotationIntegrationTests.java

@@ -0,0 +1,86 @@
+/*
+ * Copyright 2002-2019 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.test.context.junit.jupiter;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.context.ApplicationContext;
+import org.springframework.test.context.TestConstructor;
+import org.springframework.test.context.TestPropertySource;
+import org.springframework.test.context.junit.SpringJUnitJupiterTestSuite;
+import org.springframework.test.context.junit.jupiter.comics.Dog;
+import org.springframework.test.context.junit.jupiter.comics.Person;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+/**
+ * Integration tests which demonstrate support for automatically
+ * {@link Autowired @Autowired} test class constructors in conjunction with the
+ * {@link TestConstructor @TestConstructor} annotation
+ *
+ * <p>To run these tests in an IDE that does not have built-in support for the JUnit
+ * Platform, simply run {@link SpringJUnitJupiterTestSuite} as a JUnit 4 test.
+ *
+ * @author Sam Brannen
+ * @since 5.2
+ * @see SpringExtension
+ * @see SpringJUnitJupiterAutowiredConstructorInjectionTests
+ * @see SpringJUnitJupiterConstructorInjectionTests
+ */
+@SpringJUnitConfig(TestConfig.class)
+@TestPropertySource(properties = "enigma = 42")
+@TestConstructor(autowire = true)
+class TestConstructorAnnotationIntegrationTests {
+
+	final ApplicationContext applicationContext;
+	final Person dilbert;
+	final Dog dog;
+	final Integer enigma;
+
+	TestConstructorAnnotationIntegrationTests(ApplicationContext applicationContext, Person dilbert, Dog dog,
+			@Value("${enigma}") Integer enigma) {
+
+		this.applicationContext = applicationContext;
+		this.dilbert = dilbert;
+		this.dog = dog;
+		this.enigma = enigma;
+	}
+
+	@Test
+	void applicationContextInjected() {
+		assertNotNull(applicationContext, "ApplicationContext should have been injected by Spring");
+		assertEquals(this.dilbert, applicationContext.getBean("dilbert", Person.class));
+	}
+
+	@Test
+	void beansInjected() {
+		assertNotNull(this.dilbert, "Dilbert should have been @Autowired by Spring");
+		assertEquals("Dilbert", this.dilbert.getName(), "Person's name");
+
+		assertNotNull(this.dog, "Dogbert should have been @Autowired by Spring");
+		assertEquals("Dogbert", this.dog.getName(), "Dog's name");
+	}
+
+	@Test
+	void propertyPlaceholderInjected() {
+		assertNotNull(this.enigma, "Enigma should have been injected via @Value by Spring");
+		assertEquals(Integer.valueOf(42), this.enigma, "enigma");
+	}
+
+}

spring-test/src/test/java/org/springframework/test/context/support/TestConstructorUtilsTests.java

@@ -0,0 +1,106 @@
+/*
+ * Copyright 2002-2019 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.test.context.support;
+
+import java.lang.reflect.Constructor;
+
+import org.junit.After;
+import org.junit.Test;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.test.context.TestConstructor;
+
+import static org.junit.Assert.*;
+
+/**
+ * Unit tests for {@link TestConstructorUtils}.
+ *
+ * @author Sam Brannen
+ * @since 5.2
+ */
+public class TestConstructorUtilsTests {
+
+	@After
+	public void clearGlobalFlag() {
+		System.clearProperty(TestConstructor.TEST_CONSTRUCTOR_AUTOWIRE_PROPERTY_NAME);
+	}
+
+	@Test
+	public void notAutowirable() throws Exception {
+		assertNotAutowirable(NotAutowirableTestCase.class);
+	}
+
+	@Test
+	public void autowiredAnnotation() throws Exception {
+		assertAutowirable(AutowiredAnnotationTestCase.class);
+	}
+
+	@Test
+	public void testConstructorAnnotation() throws Exception {
+		assertAutowirable(TestConstructorAnnotationTestCase.class);
+	}
+
+	@Test
+	public void automaticallyAutowired() throws Exception {
+		setGlobalFlag();
+		assertAutowirable(AutomaticallyAutowiredTestCase.class);
+	}
+
+	@Test
+	public void automaticallyAutowiredButOverriddenLocally() throws Exception {
+		setGlobalFlag();
+		assertNotAutowirable(TestConstructorAnnotationOverridesGlobalFlagTestCase.class);
+	}
+
+	private void assertAutowirable(Class<?> testClass) throws NoSuchMethodException {
+		Constructor<?> constructor = testClass.getDeclaredConstructor();
+		assertTrue(TestConstructorUtils.isAutowirableConstructor(constructor, testClass));
+	}
+
+	private void assertNotAutowirable(Class<?> testClass) throws NoSuchMethodException {
+		Constructor<?> constructor = testClass.getDeclaredConstructor();
+		assertFalse(TestConstructorUtils.isAutowirableConstructor(constructor, testClass));
+	}
+
+	private void setGlobalFlag() {
+		System.setProperty(TestConstructor.TEST_CONSTRUCTOR_AUTOWIRE_PROPERTY_NAME, "true");
+	}
+
+
+	static class NotAutowirableTestCase {
+	}
+
+	@TestConstructor(autowire = false)
+	static class AutowiredAnnotationTestCase {
+
+		@Autowired
+		AutowiredAnnotationTestCase() {
+		}
+	}
+
+	@TestConstructor(autowire = true)
+	static class TestConstructorAnnotationTestCase {
+	}
+
+	static class AutomaticallyAutowiredTestCase {
+	}
+
+	@TestConstructor(autowire = false)
+	static class TestConstructorAnnotationOverridesGlobalFlagTestCase {
+	}
+
+}