### Question:
ChangeSetManagerImpl implements ChangeSetManager { @Override public ChangeSetReader getChangeSetReader(int resourceId, String driftDefinitionName) throws IOException { File changeSetFile = findChangeSet(resourceId, driftDefinitionName); if (changeSetFile == null) { return null; } return new ChangeSetReaderImpl(changeSetFile); } ChangeSetManagerImpl(File changeSetsDir); @Override boolean changeSetExists(int resourceId, Headers headers); @Override File findChangeSet(int resourceId, String driftDefinitionName); @Override File findChangeSet(int resourceId, String name, DriftChangeSetCategory type); @Override ChangeSetReader getChangeSetReader(int resourceId, String driftDefinitionName); @Override ChangeSetReader getChangeSetReader(File changeSetFile); @Override ChangeSetWriter getChangeSetWriter(int resourceId, Headers headers); @Override ChangeSetWriter getChangeSetWriter(File changeSetFile, Headers headers);  }### Answer:
@Test public void returnNullReaderWhenNoChangeSetExists() throws Exception { ChangeSetReader reader = changeSetMgr.getChangeSetReader(resourceId(), "test"); assertNull(reader, "Expect null for the reader when no change set exists for the drift definition."); }