Acceptance testing an incrementing value

Question

I have a service which returns id of the created file, and afterwards it increments the id to identify the next file. For acceptance tests we have different project, therefore when I run the test it only passes if it is the first time this service is called. Is there any workaround I can use to overcome this issue?

@Test
public void createFileServiceTest(){
    int id = service.createFile("test.xml");

    assertEquals(0, id);
}

Answer 1

Your test does not match your specification/verbal explanation of the service. So you should not look for a workaround but cleanly redesign the test (or the service, or both).

Redesigning the test, for instance

@Test
public void creatingAFileTwiceShouldYieldDifferentIDs(){
    int id1 = service.createFile("test.xml");
    int id2 = service.createFile("test.xml");

    assertThat(id1, not(equalTo(id2)));
}

@Test
public void creatingFilesShouldYieldSuccessiveIDs(){
    int id1 = service.createFile("test1.xml");
    int id2 = service.createFile("test2.xml");

    assertThat(id1+1, is(equalTo(id2)));
}

Redesigning both, making the service more testable, for instance

@Test
public void resetServiceShouldResetGetMaxId(){
    service.reset();
    assertThat(service.getMaxId(), is(equalTo(0)));
}

@Test
public void getMaxIdShouldYieldLatestId(){
    int id = service.createFile("test.xml");
    int newMaxId = service.getMaxId();

    assertThat(id, is(equalTo(newMaxId)));
}

@Test
public void creatingFilesShouldYieldSuccessiveIDs(){
    int oldMaxId = service.getMaxId();
    int id = service.createFile("test.xml");

    assertThat(oldMaxId+1, is(equalTo(id)));
}

Of course, if you have concurrent access to the service, you should guarantee atomicity of your tests, or weaken your checks from (a+1==b) to (a<b).