What is the purpose of mocks?

Mocking is a process used in unit testing when the unit being tested has external dependencies. The purpose of mocking is to isolate and focus on the code being tested and not on the behavior or state of external dependencies.

Why are stubs mocks and doubles used in unit testing?

In this article, Michał Lipski describes three types of test doubles – fake, stub and mock – and gives you examples when to use them in your unit testing. This reduces complexity, allows to verify code independently from the rest of the system and sometimes it is even necessary to execute self validating tests at all.

What are two reasons to use mock objects in unit tests?

Mock objects allow you to set up test scenarios without bringing to bear large, unwieldy resources such as databases. Instead of calling a database for testing, you can simulate your database using a mock object in your unit tests.

When should mocks be used?

TL;DR: Mock every dependency your unit test touches. Mock objects are useful when you want to test interactions between a class under test and a particular interface. For example, we want to test that method sendInvitations(MailServer mailServer) calls MailServer.

What’s the difference between a mock and a stub?

Stubs and mocks are both dummy objects for testing, while stubs only implement a pre-programmed response, mocks also pre-program specific expectations. To put it into a workflow: Stubs

Where does the data for a mock come from?

The data source of stubs is hardcoded. It is usually tightly coupled to the test suite. Data on mocks is set up by the tests. Stubs are usually handwritten, and some are generated by tools. Mocks are usually created by using the third-party library such as Mockito, JMock, and WireMock.

What’s the difference between asserts and mock objects?

The asserts the test uses are always against the class under test. On the other hand, the test will use a mock object to verify whether the test failed or not. […] Again, the mock object is the object we use to see if the test failed or not. That means if you are making assertions against the fake it means you are using the fake as a mock]

When to use a stub in a test?

Stubs are the objects that hold predefined data and uses it to give responses during tests. In other words, a stub is an object that resembles a real object with the minimum number of methods needed for a test. Stubs are used when we don’t want to use objects that would give a response with real data.