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Mock different return values mockito

By | 12.07.2020

GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together. Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community. Already on GitHub? Sign in to your account. I have mock A built and given to me. Now, I need to mock a suspend API to return a value foo. Originally posted by andrewborba10 in comment.

Testing that a mocked class returns the mocked data that I mocked for it isn't actually useful. That is to say, my suspend functions are only there to retrieve data network calls and I should focus on testing the function that contains the business logic for once those calls are returned.

Granted, if there is a way to do what you're asking for it can still be very useful and I want to know. I'm not sure if I can follow your argumentation, about not having actual business logic.

Let me try to give you an example. Let's consider A is actually called ARepowhich is a repository with the signature suspended fun getFoo : Foo. My classUnderTest calls ARepo. So, how would I mock different. I actually had it exactly this way, but I was getting compile errors. Let me double check on my project. There would still be a good reason to be able to provide suspend answers.

mock different return values mockito

For example you could have method suspend infinitely to mock server call that takes forever to complete. With mockito-kotlin This still blocks the execution, not suspend. For example if you would do delay inside onBlockingyour test will freeze for two seconds instead of suspend. I personally don't care if the test would be blocked. My main issue is, that we have the convention to mock everything out for a positive execution. And within the individual methods, we adjust the existing mocks for different preconditions.

So, from my point of view, this can be closed. For testing timeouts your code should throw Timeout Exceptions or return sealed class representing a timeout. So just use doThrow and your execution wont freeze. Beware that this is also a antipattern.Mocking and stubbing are the cornerstones of having quick and simple unit tests.

Unlike with integration or functional tests, where the real system is being tested as a whole, unit tests should focus on a single class. Everything else should be either a simple class or a mock. Mockito now seems to be the dominant Mocking framework in Java, and is now in its second version.

Spock is also a great solution that we will explore in a future article. Despite the version number, Mockito is mostly the same as Mockito 1, as far as the external API is concerned.

If you have any existing Mockito tests, you may need to change some imports. However, other than that, upgrading to Mockito should be easy regardless of your code size. It is assumed that you already have a Java project and you want to write unit tests for it. We will need:. Mockito is commonly used with JUnit.

Therefore, familiarity with JUnit is essential. It is also assumed that we already know our way around basic Maven builds. If not, then feel free to consult its official documentation first. Mockito is already distributed via Maven central, so using it in a Java forward is a painless process.

We need to modify the pom. All the examples in this article use static methods. Feel free to use annotations instead, but make sure that you agree on a single solution with the rest of your team, so that unit tests are written in a common format.

Mockito mock method with null parameter

The theory behind mocking and stubbing is so vast that it would need an entire book on its own. This tutorial will summarize the basics of it. Semaphore also provides tutorials for mocking in other languages if your interests go beyond Java:. These tests are the mainstay of your whole test suite and should comprise the bulk number of all your tests. In this article, we talk about these tests exclusively.

Some developers confuse unit tests with the second layer of the testing pyramid which is called integration tests, or service tests, or system tests, or functional tests. This distinction is important. It can become a unit test if you mock that external web service.In Mockito, you can specify what to return when a method is called. Mockito supports two ways to do it: when-thenReturn and doReturn-when.

In most cases, when-thenReturn is used and has better readability. However, sometimes you need to consider using doReturn-when because there are different behaviors. The parameter of doReturn is Object unlike thenReturn. So, there is no type checking in the compile time. This is the main reason why when-thenReturn is a better option if possible.

Although there is no type safety, the advantage of doReturn-when is no side effect. In Mockito, a side effect happens to the real method invocation. To understand this, you need to know when a real method invocation happens. Generally, you first need to create a mock object with Mockito. There is no side effect so when-thenReturn and doReturn-when acts almost the same except when-thenReturn has a type safety.

The difference comes when you create a spy with Mockito. A spied object is linked to an actual object. So, there is a real method invocation when you call a method. This is valid even for when you do when-thenReturn. This is due to a parameter of when and it contains a way to invoke a method. In contrast, a parameter of when is only user when you use doReturn-when.

For example, List get throws an exception if the list is smaller. Another example is to change a class behavior for unit testing.

AccountService is a target to test so you cannot mock it. With Mocktio. If there is no side effect, you can still use when-thenReturn for a spied object. You can use doReturn-when to specify a return value on a spied object without making a side effect.

It is useful but should be used rarely. Then, you can use more type safe and readable Mockito. No type safety The parameter of doReturn is Object unlike thenReturn. No side effect Although there is no type safety, the advantage of doReturn-when is no side effect.

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Dependency Injection

Is there a way to have a stubbed method return different objects on subsequent invocations? I'd like to do this to test nondeterminate responses from an ExecutorCompletionService. You can do that using the thenAnswer method when chaining with when :. Or using the equivalent, static doAnswer method:. You can put as many arguments as you like in the brackets of thenReturn, provided they're all the correct type.

The first value will be returned the first time the method is called, then the second answer, and so on. The last value will be returned repeatedly once all the other values are used up. As previously pointed out almost all of the calls are chainable.

More info in Mockito's Documenation. I've implemented a MultipleAnswer class that helps me to stub different answers in every call. Here the piece of code:.

Following can be used as a common method to return different arguments on different method calls. Only thing we need to do is we need to pass an array with order in which objects should be retrieved in each call. Should be used like when something. Related to [Igor Nikolaev]'s answer from 8 years ago, using an Answer can be simplified somewhat using a lambda expression available in Java 8.

Learn more. Using Mockito with multiple calls to the same method with the same arguments Ask Question. Asked 8 years, 5 months ago. Active 2 months ago. Viewed k times. The code I'm looking to test looks something like this. Emma Emma 4, 2 2 gold badges 15 15 silver badges 11 11 bronze badges. Active Oldest Votes.Comment 5. First, it encourages students to think about writing for testability by showing what kinds of designs are easy to test and what kinds are very challenging.

I believe this encourages more modular code. Second, it encourages students to write smaller, more focused unit tests. Now that so many of our systems are radically distributed, with multiple services interacting with each other, it can be challenging to think in terms of true unit testing of the business logic inside the service as opposed to just invoking the service from outside.

The problem is that tests that invoke the service from outside tend to be brittle because they usually involve network connections and service dependencies and they tend to not be as comprehensive because it's hard to generate real-world failure conditions in the context of an integration environment.

Mockito is impressive because the relatively simple, fluent API hides a wealth of complexity. To get started, let's walk through the code under test. Of course, this also has the advantage that we can use a connection pool or run this code in a Java Enterprise environment. What makes this challenging for testing is that there are multiple interfaces involved.

I've done both of these in creating integration tests, but neither is really a proper unit test approach. Instead, we can use Mockito to create a "mock object" for each of these items. The mock object is a dynamically generated object that pretends to implement some interface or be an instance of some class, typically using a library like ASM.

Let's take some time to walk through each part of this code in order to understand what's going on. First, we see an annotation on the class:. Ordinarily, when we run a JUnit test, we tell JUnit about our class and it uses reflection to inspect it for annotations.

A mock object, as I said above, is a dynamic object that pretends to implement an interface or be an instance of a class. I say "pretends to" because there isn't any Java source code you can point to that implements the interface or provides any instance methods.

Instead, there is generic code that is invoked, no matter what method is called. This interceptor in Mockito looks at any specific configuration that might have taken place for that mock object, or falls back to some default behavior.

This behavior lets us get pretty far without having to do any additional configuration. Where the default behavior won't work, we can tell Mockito what to do differently. This is where the fluent API is fun to use. Once we've got the knack, we can write statements like this:.

For methods that take arguments, Mockito has a sophisticated matching scheme.

mock different return values mockito

The simplest is to allow any argument to match:. Note that in this example we do just enough work to make sure things behave as expected.

Of course, this has the potential to make our test brittle, because there are lots of changes to the code under test that would cause the test to incorrectly report failure.

We have to trade off between improving the realism of the test and its simplicity. In the next article, I'll show a more complex example where we pay closer attention to some of the parameters we receive and use them to make the behavior of the mocks more realistic. Over a million developers have joined DZone. Let's be friends:. DZone 's Guide to.

mock different return values mockito

Object mocking frameworks use complex code generation and reflection to cut out a lot of boilerplate test code.A unit test should test functionality in isolation. Side effects from other classes or the system should be eliminated for a unit test, if possible. This can be done via using test replacements test doubles for the real dependencies. Test doubles can be classified like the following:. A dummy object is passed around but never used, i. Such an object can for example be used to fill the parameter list of a method.

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Fake objects have working implementations, but are usually simplified. For example, they use an in memory database and not a real database. A stub class is an partial implementation for an interface or class with the purpose of using an instance of this stub class during testing.

Stubs may also record information about calls. A mock object is a dummy implementation for an interface or a class in which you define the output of certain method calls.

Mock objects are configured to perform a certain behavior during a test. They typically record the interaction with the system and tests can validate that.

Test doubles can be passed to other objects which are tested. Your tests can validate that the class reacts correctly during tests. For example, you can validate if certain methods on the mock object were called. This helps to ensure that you only test the class while running tests and that your tests are not affected by any side effects.

You can create mock objects manually via code or use a mock framework to simulate these classes. Mock frameworks allow you to create mock objects at runtime and define their behavior. The classical example for a mock object is a data provider. In production an implementation to connect to the real data source is used.

But for testing a mock object simulates the data source and ensures that the test conditions are always the same. These mock objects can be provided to the class which is tested.

Therefore, the class to be tested should avoid any hard dependency on external data. Mocking or mock frameworks allows testing the expected interaction with the mock object. You can, for example, validate that only certain methods have been called on the mock object. Mockito is a popular mock framework which can be used in conjunction with JUnit. Mockito allows you to create and configure mock objects.

mock different return values mockito

Using Mockito greatly simplifies the development of tests for classes with external dependencies. Maven users can declare a dependency. Search for g:"org. These build system allow to manage your software dependencies. Therefore, you are advised to use either the Gradle or Maven tooling in Eclipse. If you are using IntelliJ, you should use either Gradle or Maven to manage your dependencies to Mockito.Comment Most of the classes we come across have dependencies, and oftentimes, methods delegate some work to other methods in other classes.

These classes are our dependencies. When unit testing such methods, if we only use JUnit, our tests will also depend on those methods as well. We want the unit tests to be independent of all other dependencies. Mockito is a mocking framework that tastes really good. So, going back to the example above, how do we mock out the dependency using Mockito? Well, we could inject a mock to the class under test instead of the real implementation while we run our tests!

The following is the test that mocks the dependency using Mockito:. Now we have successfully created and injected the mock, and now we should tell the mock how to behave when certain methods are called on it. The following is an example of how to use it. Bear in mind, it isn't an ideal use case, but I wanted to illustrate the basic usage:.

Methods with return values can be tested by asserting the returned value, but how do we test void methods? The void method that you want to test could either be calling other methods to get things done, processing the input parameters, or maybe generating some values or all of it.

With Mockito, you can test all of the above scenarios. A great thing about mocking is that we can verify that certain methods have been called on those mock objects during test execution — in addition to or in place of assertions — when the method under test is void.

A Guide to Mocking With Mockito

ArgumentCaptor :. Please check out the below websites for more cool features, best practices, and guidelines on Mockito. Official Mockito website. Mockito Main reference documentation. Wiki page. Published at DZone with permission of Dilini Rajapaksha. See the original article here. Over a million developers have joined DZone.

Let's be friends:. A Guide to Mocking With Mockito. DZone 's Guide to. If you're thinking about trying Mockito out for unit testing, this article provides a comprehensive guide to injecting mocks and mocking methods, including void methods.


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