Introduce @ForkedClassPath for testing unmodified class path

See gh-22710

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

@@ -0,0 +1,37 @@
+/*
+ * Copyright 2012-2020 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.classpath;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link ForkedClassPath @ForkedClassPath}.
+ *
+ * @author Christoph Dreis
+ */
+@ForkedClassPath
+class ModifiedClassPathExtensionForkTests {
+
+	@Test
+	void modifiedClassLoaderIsUsed() {
+		ClassLoader classLoader = getClass().getClassLoader();
+		assertThat(classLoader.getClass().getName()).isEqualTo(ModifiedClassPathClassLoader.class.getName());
+	}
+
+}