Using mockConstruction with ProcessBuilder

[Roman Levin]

Sorry if this is an incredibly basic question, but I'm new to Java, as well as to Mockito.

I'm using mockConstruction to mock out ProcessBuilder. What I don't understand is the proper way to configure the behavior of the Process mock that is returned when ProcessBuilder::start() is called.

In code form, I'm trying to do something like this:

void testedFunction() {

  String[] cmd = {"foo"};

  ProcessBuilder pb = ProcessBuilder("foo");

  Process process = pb.start();

  

  // How do I, for example, make `finished == true` here?

  boolean finished = process.waitFor(5, TimeUnit.SECONDS))

}

@Test

void test() {

  try (MockedConstruction<ProcessBuilder> mocked = mockConstruction(ProcessBuilder.class, withSettings().defaultAnswer(RETURNS_MOCKS))) {

    testedFunction();

  }

}

This question is applicable to any builder-patterned type, I guess, but I thought it would be better to be specific.

[Tim van der Lippe]

Rather than using `RETURNS_MOCKS`, you want more control over your mocks (good!). Therefore, I would change it such that you return a new mock for the `start` invocation. Then you can make sure that the `waitFor` on the mock (you just defined), returns what you want (in this case `true`).

Op do 10 sep. 2020 om 14:19 schreef Roman Levin <roman...@gmail.com>:

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[Roman Levin]

On Thursday, September 10, 2020 at 5:49:28 PM UTC+2 tvande...@gmail.com wrote:

I would change it such that you return a new mock for the `start` invocation.

Thanks for your reply! Yeah, that's what I want to do, but I'm just not sure what the right incantation is to do that. Do I define a custom Answer? If so, could you maybe point me at the appropriate documentation for doing this correctly? I kind of tried to reverse engineer it from the Mockito source code, but I just don't have enough context to easily figure it out on my own.

[Roman Levin]

For the record, had to do something like:

MockedConstruction<ProcessBuilder> mocked = mockConstruction(
    ProcessBuilder.class,
    context -> new MockSettingsImpl<>().defaultAnswer(RETURNS_MOCKS),
    (builderMock, context) -> {
        Process processMock = mock(Process.class);
        when(builderMock.start()).thenReturn(processMock);
        when(processMock.waitFor(5L, TimeUnit.SECONDS)).thenReturn(true);

...

Don't know if it's the minimal or most elegant solution, but it works.