FileCreatorTestWithCustomValidator.java

public class FileCreatorTestWithCustomValidator {

    private FileCreator fileCreator = new FileCreator();

    private String fileName = "file.txt";

    @Before
    public void setUp() throws IOException {
        Files.deleteIfExists(Paths.get(fileName));
    }

    @Test
    public void shouldCreateFile() throws InterruptedException {
        // when
        fileCreator.createFile(fileName);

        // then
        boolean fileExists = checkThatFileExists(fileName);
        assertThat(fileExists, is(true));
    }

    private boolean checkThatFileExists(String fileName) 
            throws InterruptedException {
        for (int i = 0; i < 100; i++) {
            Path path = Paths.get(fileName);
            try {
                assertThat(path, exists());
                return true;
            } catch (AssertionError e) {
                // ignore exception
            }
            Thread.sleep(100);
        }
        throw new AssertionError("Timeout exceeded");
    }
}