单元测试状态

Question

I am trying to fetch data from SharedPreferences during initState() and test it. If I simply set private variable inside the state without invoking setState(), view is not updated.

If I try to wrap setting variables inside setState() my test will break with null pointer at setState() method.

NoSuchMethodError: The method 'markNeedsBuild' was called on null.
Receiver: null
Tried calling: markNeedsBuild()

Here is my initState()

initState() {
  _appRepository.readOnboardingCompleted().then((readValue) {
    print("read: $readValue");
    setState(()=>_onboardingCompleted = readValue);
});
  super.initState();
}

here is the test

test(
  'GIVEN app starts WHEN onboarding was completed THEN onboarding is disabled',() {

     when(mockAppRepository.readOnboardingCompleted()).thenReturn(mockBoolFuture);
     AppState systemUnderTest = new AppState(mockAppRepository);
     systemUnderTest.initState();
     verify(mockAppRepository.readOnboardingCompleted());
});

I feel there has to be an easier way of doing this.

Answer 1

Use SharedPreferences.setMockInitialValues to initialize SharedPreferences with values for testing. Then you don't need to mock it yourself.

I don't think unit testing the behavior of initState is the right way to achieve your code coverage goals. A State is tied to a StatelessWidget . The public API of the StatelessWidget is its constructor arguments (input) and the render objects it produces (output). Nobody should be calling protected methods of a State like initState except for Flutter itself.

I suggest you take a look at the Flutter unit tests and see if you can write tests that are more at that level, eg icon button test .