How to create a list of dummy files in Java?

Question

I need to create a List<File> files, so that it contains 3 dummy files. How do I do that?

I need that for unit test.

I did

private File file1 = mock(File.class);
private File file2 = mock(File.class);
private File file3 = mock(File.class);

List<File> files = Lists.newArrayList(file1, file2, file3);

But I thought is is all possible in one line.

Answer 1

I would recommend not mocking File and instead make fake values. Methods that act on File instances tend to care about the file path and/or whether the file exists, so the most straight-forward way to do that is to use real instances.

Here is an example using JUnit4 that creates a list of three File instances to refer to files that don't exist in a directory that does:

@RunWith(JUnit4.class)
public class ExampleTest {
  @Rule
  public TemporaryFolder testFolder = new TemporaryFolder();

  private final Foo foo = new Foo();

  @Test
  public void shouldFailIfFilesDoNotExist() {
    List<File> files = Lists.newArrayList(
        testFolder.newFile(),
        testFolder.newFile(),
        testFolder.newFile());
    foo.doIt(files);
  }
}

If you care about the filenames, you can pass the name of the file to TemporaryFolder.newFile(String)