Mock a private static field with JMockit?

Question

I have a class like the following;

class ClassA {
    private static File myDir;

    // myDir is created at some stage

    private static String findFile(final String fileName) {
       for (final String actualBackupFileName : myDir.list()) {
           if (actualBackupFileName.startsWith(removeExtensionFrom(backupFile))) {
               return actualBackupFileName;
            }
       }
    }
}

So, basically, I want to test this class by mocking out the File class so that when list() is called on it it returns a list of strings I define in my test class.

I've got the following but its not working at the minute, there's probably something obvious I'm doing wrong - I'm new to JMockit - any help is much appreciated!

@Mocked("list") File myDir;

@Test
  public void testClassA() {
    final String[] files = {"file1-bla.txt"};

    new NonStrictExpectations() {{
      new File(anyString).list(); 
      returns(files);
   }};

   String returnedFileName = Deencapsulation.invoke(ClassA.class, "findFile","file1.txt");

   // assert returnedFileName is equal to "file1-bla.txt"
  }

When running the above test I get a NullPointerException for the myDir field in ClassA - so it looks like its not getting mocked properly?

Answer 1

You can use the setField method from the Deencapsulation class. Note example below:

Deencapsulation.setField(ClassA, "File", your_desired_value);