JUnit for a method with while loop

Question

I am facing some difficulty in writing a JUnit test for a method with a While loop. My method looks like below:

private void deleteMethod(DeleteRequest dr){

    // below statement am calling some service which returns me a object after querying it from Database.
    SomeObject ob = db.getdata(dr);

    while(ob != null) {
        // this method deletes the Data from DB 
        db.deleteData(ob);
        // again calling the same service operation as we did before while loop. I have a situation where my service only returns single record at a time. It is avoidable that I need to do a dirty job.
        ob = db.getdata(dr);
    }

Below is my JUnit:

@Test
public void testDeleteMethod() throws Exception{
    DeleteRequest mockDR = new DeleteRequest();
    mockDR.setX(y);
    SomeObject mockOB = new SomeObject();
    mockOB.setZ(k);
    // making a mockcall to the method before I can assert anything
    mockClassObject.deleteMethod(mockDR); 
}

The above JUnit method is getting struck in execution for ever and I understand that its not getting out of the while loop. How I can approach this issue. Just to mention am using Mockito framework and am not aware if at all there is any way to handle this situation in Mockito.

Answer 1

Using Mockito, you have to mock the db connection and inject it into your service using @InjectMocks, constructor injection, or via a setter before you test your method. This is how I would write your test.

@Test
public void testDeleteMethod() throws Exception{
    DeleteRequest deleteRequest = new DeleteRequest();
    deleteRequest.setX(y);
    SomeObject someObject = new SomeObject();
    someObject.setZ(k);

    Database db = Mockito.mock(Database.class);
    // Notice chain of calls
    Mockito.when(db.getdata(deleteRequest))
        .thenReturn(someObject).thenReturn(null);

    // TODO Inject the Database object into your mockClassObject.

    // making a mock call to the method before I can assert anything
    mockClassObject.deleteMethod(deleteRequest);

    Mockito.verify(db, Mockito.times(2)).getdata(deleteRequest);
    Mockito.verify(db).deleteData(someObject);
}

You can see that I chain the calls on the db.getData() method two times, the first time returns someObject and the second time returns null.