[hotfix] Simplify tests in ClassLoaderITCase

This also makes child-first classloading explicit in the test instead of
relying on the default.

flink-tests/src/test/java/org/apache/flink/test/classloading/ClassLoaderITCase.java

@@ -395,7 +395,7 @@ public void testProgramWithChildFirstClassLoader() throws IOException, ProgramIn
  String childResourceDirName = "child0";
  String testResourceName = "test-resource";
  File childResourceDir = FOLDER.newFolder(childResourceDirName);
- File childResource = new File(childResourceDir.getAbsolutePath() + File.separator + testResourceName);
+ File childResource = new File(childResourceDir, testResourceName);
  assertTrue(childResource.createNewFile());
 
  TestStreamEnvironment.setAsContext(
@@ -404,10 +404,14 @@ public void testProgramWithChildFirstClassLoader() throws IOException, ProgramIn
  Collections.singleton(new Path(CLASSLOADING_POLICY_JAR_PATH)),
  Collections.emptyList());
 
- // default child first classloading
+ // child-first classloading
+ Configuration childFirstConf = new Configuration();
+ childFirstConf.setString("classloader.resolve-order", "child-first");
+
  final PackagedProgram childFirstProgram = PackagedProgram.newBuilder()
  .setJarFile(new File(CLASSLOADING_POLICY_JAR_PATH))
  .setUserClassPaths(Collections.singletonList(childResourceDir.toURI().toURL()))
+ .setConfiguration(childFirstConf)
  .setArguments(testResourceName, childResourceDirName)
  .build();
 
@@ -427,15 +431,14 @@ public void testProgramWithParentFirstClassLoader() throws IOException, ProgramI
  String childResourceDirName = "child1";
  String testResourceName = "test-resource";
  File childResourceDir = FOLDER.newFolder(childResourceDirName);
- File childResource = new File(childResourceDir.getAbsolutePath() + File.separator + testResourceName);
+ File childResource = new File(childResourceDir, testResourceName);
  assertTrue(childResource.createNewFile());
 
  TestStreamEnvironment.setAsContext(
  miniClusterResource.getMiniCluster(),
  parallelism,
  Collections.singleton(new Path(CLASSLOADING_POLICY_JAR_PATH)),
  Collections.emptyList());
- final ClassLoader contextClassLoader = Thread.currentThread().getContextClassLoader();
 
  // parent-first classloading
  Configuration parentFirstConf = new Configuration();
@@ -448,6 +451,7 @@ public void testProgramWithParentFirstClassLoader() throws IOException, ProgramI
  .setArguments(testResourceName, "test-classes")
  .build();
 
+ final ClassLoader contextClassLoader = Thread.currentThread().getContextClassLoader();
  Thread.currentThread().setContextClassLoader(parentFirstProgram.getUserCodeClassLoader());
  try {
  parentFirstProgram.invokeInteractiveModeForExecution();