Test doubles

- [Instructor] What happens if we run…this test again?…Let's try that.…Click on the green triangle to run…click to favorite again.…This time it failed.…Let's take a look at the error message.…It said, expected, not is selected,…and then has this long list of attributes.…If you scroll you can see…that the view is selected is actually true.…Scroll down in the errors…and see where the failure actually happens.…

It's in line 45.…We are verifying that we started…with the recipe as not selected.…And the reason why it failed is because,…when we ran this test previously…we clicked on the recipe…and stored the variables selected…into our shared preferences.…This is why when we run the test a second time…it will not pass.…When the test changes the state of the app,…we cannot run it again…and expect the same result.…

How to solve this problem?…We want it so that in the app…it will always remember our selection,…but in our test, we want it to start…as a known state.…To solve this problem…we can use dependency injection…with test doubles.…