Migrate JUnit 3 tests to JUnit 4

This commit migrates all remaining tests from JUnit 3 to JUnit 4, with
the exception of Spring's legacy JUnit 3.8 based testing framework that
is still in use in the spring-orm module.

Issue: SPR-13514

spring-core/src/main/java/org/springframework/util/StopWatch.java

@@ -72,7 +72,7 @@ public class StopWatch {
 	 * Construct a new stop watch. Does not start any task.
 	 */
 	public StopWatch() {
-		this.id = "";
+		this("");
 	}
 
 	/**