JUnit Testing multiple functions at once

Question

I am trying to make some Junit tests for a tic tac toe board. I know how to test one function at a time, but my problem is that in order to check some function, previous functions must be called.

For example, in order to check a winner, you have to call the function "PlaceMarker" function multiple times. The specific one I'm on is checking to make sure the bool function "CheckSpace" returns false when there is already a marker in the spot its checking. I currently have

public class TestGame {

private GameBoard board;

@Before
public void setUp() {board = new GameBoard();}

@After
public void tearDown() {board = null;}

@Test
public void testRewritingOverSpace() {
  assertEquals("Placing (1, 1), then checking space (1, 1)", false,
  board.placeMarker(new BoardPosition(1, 1, 'X')),
  board.checkSpace(new BoardPosition(1, 1, 'O'));

This is giving me a error. So in short, how do you make a JUnit test case in which you have to call multiple functions.

"This is giving me a error." Without knowing what the error is, it's very hard to help you. It's not clear what assertion you're expecting to make here, to be honest. Perhaps you want to call board.placeMarker(...) and then assertEquals(false, board.checkSpace(...))? Is it the checkSpace method that you're testing in terms of returning false? — Jon Skeet
– Jon Skeet, Commented Oct 19, 2017 at 15:22
Please provide more details regarding the error you are seeing as well as the version of JUnit you are using. — D.B.
– D.B., Commented Oct 19, 2017 at 15:46
Questions seeking debugging help ("why isn't this code working?") must include the desired behavior, a specific problem or error and the shortest code necessary to reproduce it in the question itself. Questions without a clear problem statement are not useful to other readers. See: How to create a minimal reproducible example. Use the "edit" link to improve your question - do not add more information via comments. Thanks! — GhostCat
– GhostCat, Commented Oct 20, 2017 at 9:21

GhostCat · Accepted Answer · 2017-10-20 09:33:03Z

To answer the question: you go step by step. Especially when you consider TDD, you work like this:

you create a first test for the very first "feature" of your production code
you implement that feature
you write another test ... and implement

And yes, that could mean that your code looks like:

@Test
public void testFirstFeature() {
  ... one line of setup
  ... invoke method on object under test
  ... assert something
} ...

@Test
public void testMoreAdvancedFeature() {
  ... multiple 
  ...   lines
  ...       of setup

  ... invoke method on object under test
  ... assert something
}

And you will probably find that your later test cases do actually test/verify behaviour that is already covered by tests you wrote earlier on. Then you can step back and ask yourself: "is there some merit in keeping this earlier tests - or can I safely throw them away?"

You are correct, balancing is required here: having multiple tests that do the same/similar things leads to "duplication". On the other hand - the more tests you have, the easier it will be for you to change small things here and there - and then receive immediate feedback.

Thus: there is no single answer to this. It is all about context and engineering judgement.

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