Add JUnit 5 ModifiedClassPathExtension

Add a JUnit 5 extension that allows tests to be run with a
modified classpath. Since JUnit 5 does not currently offer a way
to run tests with a different classpath, we instead fake the
original invocation and launch an entirely new run for each
method.

See gh-17491

spring-boot-project/spring-boot-tools/spring-boot-test-support/src/test/java/org/springframework/boot/testsupport/runner/classpath/ModifiedClassPathExtensionExclusionsTests.java

@@ -0,0 +1,53 @@
+/*
+ * Copyright 2012-2019 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.boot.testsupport.runner.classpath;
+
+import org.hamcrest.Matcher;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.hamcrest.Matchers.isA;
+
+/**
+ * Tests for {@link ModifiedClassPathExtension} excluding entries from the class path.
+ *
+ * @author Christoph Dreis
+ */
+@ExtendWith(ModifiedClassPathExtension.class)
+@ClassPathExclusions("hibernate-validator-*.jar")
+class ModifiedClassPathExtensionExclusionsTests {
+
+	private static final String EXCLUDED_RESOURCE = "META-INF/services/" + "javax.validation.spi.ValidationProvider";
+
+	@Test
+	void entriesAreFilteredFromTestClassClassLoader() {
+		assertThat(getClass().getClassLoader().getResource(EXCLUDED_RESOURCE)).isNull();
+	}
+
+	@Test
+	void entriesAreFilteredFromThreadContextClassLoader() {
+		assertThat(Thread.currentThread().getContextClassLoader().getResource(EXCLUDED_RESOURCE)).isNull();
+	}
+
+	@Test
+	void testsThatUseHamcrestWorkCorrectly() {
+		Matcher<IllegalStateException> matcher = isA(IllegalStateException.class);
+		assertThat(matcher.matches(new IllegalStateException())).isTrue();
+	}
+
+}

spring-boot-project/spring-boot-tools/spring-boot-test-support/src/test/java/org/springframework/boot/testsupport/runner/classpath/ModifiedClassPathExtensionOverridesTests.java

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+/*
+ * Copyright 2012-2019 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.boot.testsupport.runner.classpath;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+
+import org.springframework.context.ApplicationContext;
+import org.springframework.util.StringUtils;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link ModifiedClassPathExtension} overriding entries on the class path.
+ *
+ * @author Christoph Dreis
+ */
+@ExtendWith(ModifiedClassPathExtension.class)
+@ClassPathOverrides("org.springframework:spring-context:4.1.0.RELEASE")
+class ModifiedClassPathExtensionOverridesTests {
+
+	@Test
+	void classesAreLoadedFromOverride() {
+		assertThat(ApplicationContext.class.getProtectionDomain().getCodeSource().getLocation().toString())
+				.endsWith("spring-context-4.1.0.RELEASE.jar");
+	}
+
+	@Test
+	void classesAreLoadedFromTransitiveDependencyOfOverride() {
+		assertThat(StringUtils.class.getProtectionDomain().getCodeSource().getLocation().toString())
+				.endsWith("spring-core-4.1.0.RELEASE.jar");
+	}
+
+}