Remove JUnit 4 dependency from all modules except spring-test

This commit removes the JUnit 4 dependency from all modules except
spring-test which provides explicit JUnit 4 support.

This commit also includes the following.

- migration from JUnit 4 assertions to JUnit Jupiter assertions in all
  Kotlin tests
- migration from JUnit 4 assumptions in Spring's TestGroup support to
  JUnit Jupiter assumptions, based on org.opentest4j.TestAbortedException
- introduction of a new TestGroups utility class than can be used from
  existing JUnit 4 tests in the spring-test module in order to perform
  assumptions using JUnit 4's Assume class

See gh-23451

spring-core/src/test/java/org/springframework/core/io/ResourceTests.java

@@ -27,7 +27,7 @@ import java.nio.file.Path;
 import java.nio.file.Paths;
 import java.util.HashSet;
 
-import org.junit.Ignore;
+import org.junit.jupiter.api.Disabled;
 import org.junit.jupiter.api.Test;
 
 import org.springframework.util.FileCopyUtils;
@@ -218,7 +218,8 @@ public class ResourceTests {
 		assertThat(relative).isEqualTo(new UrlResource("file:dir/subdir"));
 	}
 
-	@Ignore @Test // this test is quite slow. TODO: re-enable with JUnit categories
+	@Disabled
+	@Test // this test is quite slow. TODO: re-enable with JUnit categories
 	public void testNonFileResourceExists() throws Exception {
 		Resource resource = new UrlResource("https://www.springframework.org");
 		assertThat(resource.exists()).isTrue();

spring-core/src/test/java/org/springframework/tests/Assume.java

@@ -19,14 +19,14 @@ package org.springframework.tests;
 import java.util.Set;
 
 import org.apache.commons.logging.Log;
-import org.junit.AssumptionViolatedException;
 
-import static org.junit.Assume.assumeFalse;
+import static org.junit.jupiter.api.Assumptions.assumeFalse;
+import static org.junit.jupiter.api.Assumptions.assumeTrue;
 
 /**
- * Provides utility methods that allow JUnit tests to {@link org.junit.Assume} certain
- * conditions hold {@code true}. If the assumption fails, it means the test should be
- * skipped.
+ * Provides utility methods that allow JUnit tests to assume certain conditions
+ * hold {@code true}. If the assumption fails, it means the test should be
+ * aborted.
  *
  * <p>Tests can be categorized into {@link TestGroup}s. Active groups are enabled using
  * the 'testGroups' system property, usually activated from the gradle command line:
@@ -35,8 +35,8 @@ import static org.junit.Assume.assumeFalse;
  * gradle test -PtestGroups="performance"
  * </pre>
  *
- * <p>Groups can be specified as a comma separated list of values, or using the pseudo group
- * 'all'. See {@link TestGroup} for a list of valid groups.
+ * <p>Groups can be activated as a comma separated list of values, or using the
+ * pseudo group 'all'. See {@link TestGroup} for a list of valid groups.
  *
  * @author Rob Winch
  * @author Phillip Webb
@@ -44,6 +44,8 @@ import static org.junit.Assume.assumeFalse;
  * @since 3.2
  * @see #group(TestGroup)
  * @see #group(TestGroup, Executable)
+ * @see TestGroup
+ * @see TestGroups
  */
 public abstract class Assume {
 
@@ -51,29 +53,27 @@ public abstract class Assume {
 
 
 	/**
-	 * Assume that a particular {@link TestGroup} has been specified.
-	 * @param group the group that must be specified
-	 * @throws AssumptionViolatedException if the assumption fails
+	 * Assume that a particular {@link TestGroup} is active.
+	 * @param group the group that must be active
+	 * @throws org.opentest4j.TestAbortedException if the assumption fails
 	 */
 	public static void group(TestGroup group) {
-		Set<TestGroup> testGroups = loadTestGroups();
-		if (!testGroups.contains(group)) {
-			throw new AssumptionViolatedException("Requires unspecified group " + group + " from " + testGroups);
-		}
+		Set<TestGroup> testGroups = TestGroups.loadTestGroups();
+		assumeTrue(testGroups.contains(group),
+			() -> "Requires inactive test group " + group + "; active test groups: " + testGroups);
 	}
 
 	/**
-	 * Assume that a particular {@link TestGroup} has been specified before
-	 * executing the supplied {@link Executable}.
+	 * Assume that a particular {@link TestGroup} is active before executing the
+	 * supplied {@link Executable}.
 	 * <p>If the assumption fails, the executable will not be executed, but
-	 * no {@link AssumptionViolatedException} will be thrown.
-	 * @param group the group that must be specified
+	 * no {@link org.opentest4j.TestAbortedException} will be thrown.
+	 * @param group the group that must be active
 	 * @param executable the executable to execute if the test group is active
 	 * @since 4.2
 	 */
 	public static void group(TestGroup group, Executable executable) throws Exception {
-		Set<TestGroup> testGroups = loadTestGroups();
-		if (testGroups.contains(group)) {
+		if (TestGroups.loadTestGroups().contains(group)) {
 			executable.execute();
 		}
 	}
@@ -81,28 +81,13 @@ public abstract class Assume {
 	/**
 	 * Assume that the specified log is not set to Trace or Debug.
 	 * @param log the log to test
-	 * @throws AssumptionViolatedException if the assumption fails
+	 * @throws org.opentest4j.TestAbortedException if the assumption fails
 	 */
 	public static void notLogging(Log log) {
 		assumeFalse(log.isTraceEnabled());
 		assumeFalse(log.isDebugEnabled());
 	}
 
-	/**
-	 * Load test groups dynamically instead of during static
-	 * initialization in order to avoid a {@link NoClassDefFoundError}
-	 * being thrown while attempting to load the {@code Assume} class.
-	 */
-	private static Set<TestGroup> loadTestGroups() {
-		try {
-			return TestGroup.parse(System.getProperty(TEST_GROUPS_SYSTEM_PROPERTY));
-		}
-		catch (Exception ex) {
-			throw new IllegalStateException("Failed to parse '" + TEST_GROUPS_SYSTEM_PROPERTY
-					+ "' system property: " + ex.getMessage(), ex);
-		}
-	}
-
 
 	/**
 	 * @since 4.2

spring-core/src/test/java/org/springframework/tests/AssumeTests.java

@@ -18,10 +18,10 @@ package org.springframework.tests;
 
 import java.util.Arrays;
 
-import org.junit.AssumptionViolatedException;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
+import org.opentest4j.TestAbortedException;
 
 import static java.util.stream.Collectors.joining;
 import static org.assertj.core.api.Assertions.assertThat;
@@ -77,7 +77,7 @@ public class AssumeTests {
 		try {
 			Assume.group(LONG_RUNNING);
 		}
-		catch (AssumptionViolatedException ex) {
+		catch (TestAbortedException ex) {
 			fail("assumption should NOT have failed");
 		}
 	}

spring-core/src/test/java/org/springframework/tests/TestGroups.java

@@ -0,0 +1,58 @@
+/*
+ * 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.tests;
+
+import java.util.Set;
+
+/**
+ * Utility methods for working with {@link TestGroup}s.
+ *
+ * @author Sam Brannen
+ * @author Rob Winch
+ * @author Phillip Webb
+ * @since 5.2
+ */
+public abstract class TestGroups {
+
+	static final String TEST_GROUPS_SYSTEM_PROPERTY = "testGroups";
+
+
+	/**
+	 * Determine if the provided {@link TestGroup} is active.
+	 * @param group the group to check
+	 * @since 5.2
+	 */
+	public static boolean isGroupActive(TestGroup group) {
+		return loadTestGroups().contains(group);
+	}
+
+	/**
+	 * Load test groups dynamically instead of during static initialization in
+	 * order to avoid a {@link NoClassDefFoundError} being thrown while attempting
+	 * to load the {@link Assume} class.
+	 */
+	static Set<TestGroup> loadTestGroups() {
+		try {
+			return TestGroup.parse(System.getProperty(TEST_GROUPS_SYSTEM_PROPERTY));
+		}
+		catch (Exception ex) {
+			throw new IllegalStateException("Failed to parse '" + TEST_GROUPS_SYSTEM_PROPERTY
+					+ "' system property: " + ex.getMessage(), ex);
+		}
+	}
+
+}