Unlike mocks, fake implementations give us complete command over the dependencies in unit exams, allowing you to precisely and completely taste reactive moves.

At OkCupid, we quite often use the Mockito library for producing mocks of our own dependencies to be utilized inside our JUnit examinations. This permits us to conveniently mock return standards for several practices, or to verify a way ended up being also known as on one your dependencies, but it can provide issues as the integration amongst the part under ensure that you the dependencies be complicated.

In this post, were gonna walk through a limitation located making use of a mocking collection, and talk about how exactly we had the ability to see through that limitation through our personal artificial implementation. Lets begin by position the stage the complications.

Placing The Period

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Before we talk about the difficulty, lets verify we see the part under examination. Well be looking at a ViewModel that will be in charge of producing a system demand and revealing some listings.

Down the page is the snippet for ViewModel, however, if youd want to see the associated courses, you can find all of them inside gist. Keep in mind that in this ViewModel, when it’s produced, we request account suggestions inside the init process:

The moment all of our ViewModel is generated, well produce a loading condition to your LiveData. Subsequently, well request a profile, and publish a fresh ProfileViewState when the call succeeds or fails.

That is everything we truly need for our element under test. Next we can test it.

Screening The ViewModel

Well start out with one positive case examination to make sure that as soon as we ask a user, a loading county was emitted accompanied by a data county. Lets see what that test appears like:

If youd want to see the implementation of .testObserver() you will find they within gist .

The Test Fails

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To the wonder, this examination will give up! We are mocking a successful information consult, therefore we should expect which our observedStates features two records: one the loading state, plus one your profitable information condition. Upon running the exam, one assertion fails. Our test states that observedStates.size is one, therefore the advantages could be the facts state.

To phrase it differently, our test wasn’t in a position to verify that a loading state occurred.

What Happened?

Lets think of whats different within our unit examination than genuine rule. Within our device test, were moving Scheduler.trampoline() from RxJava that will help to help make the network consult operate as if they are sequential. In terms of this examination, it’s as if the system request succeeds instantly once the ViewModel is established.

Subsequently, after all of our ViewModel is made, we use a test observer on ViewModel.state LiveData, and that is currently in a loaded facts county. This implies the loading county took place too much in the time – we cannot discover a LiveData before it’s produced, therefore there is no chance to confirm a loading county actually ever happened.

This complication is due to our very own mocking collection, which says to our very own mock repository to go back information at once. Alternatively, we could establish our own artificial implementation of a ProfileRepository that we need full power over, might controls that emission of data to ensure the unit examination catches the running county.

Producing A Fake

Generate an artificial implementation, we start with generating another class that implements our very own program. Keep in mind, we dont wish all of our phony to go back data at once, for the reason that it will simply cause the exact same difficulties. As an alternative, since were making use of RxJava, we could put into action our fake such that makes use of a BehaviorSubject behind the scenes that people can manage.

The implementation you use right here may change if you use coroutines, although principle remains the exact same: we dont need to go back from fetchProfile() with information overnight. We should guarantee that the fake execution manages precisely when that information is released.

Regulating Data Emissions

Since our phony implementation is utilizing a BehaviorSubject once the fundamental data source, we can build our very own public solution to give off to they if we like:

Updating Studies To Validate Running Condition

Since we have something in position where we fine grained control of when information is emitted from our repository, we can control this to correctly sample the loading condition. Well follow this dish:

  1. Create all of our artificial repository and ViewModel part
  2. Since the fake does not produce information straight away, we will be able to confirm that individuals have been in a running state.
  3. We can get a handle on the phony execution to produce information.
  4. Final, we could examine which our ViewModel happens to be in a crammed data state.


Mocking libraries provide a fast option for producing dependencies to make use of within Android os product studies, but arrive at the cost of creating restrictions for managing the conduct of the dependencies. By leveraging interfaces and our very own phony execution that is out there within laws base, we now have full control of the dependencies and then we may use that to control the emission of data for reactive flows to thoroughly see page unit try our equipment.

I really hope you discovered this helpful! If you have some other examples of using a phony versus a mock, inform me on Twitter.

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