Mocks vs. Stubs: Choosing the Right Tool for the Job

When it comes to unit testing in software development, understanding the difference between Mocks and Stubs is crucial for ensuring effective test coverage. Both are essential tools used to simulate the behavior of dependencies in your code, but they serve different purposes. Knowing when to use Mocks vs. Stubs can help you create more reliable and maintainable tests, ultimately leading to better software quality

What are Test Doubles?

Test doubles are simplified stand-in versions of software components used in testing to simulate the behavior of real components. They help isolate the unit beneath the check via changing dependencies that aren’t the focus of the test. There are numerous forms of test doubles, consisting of mocks and stubs, each serving specific purposes. Mocks are used to affirm interactions and behaviors, while stubs provide predefined responses to method calls without imposing strict conduct verification.

What is Stub?

A stub is like a stand-in actor who says a few lines but doesn't do much else. In programming, a stub is a simple version of a part of the program that gives a basic response. We use stubs when we want to test something without needing the real part that does the work.

The objects known as "stubs" store specified data and utilize it to generate replies for tests. In other terms, a stub is an object that looks like a genuine object but only has the methods required for testing. When we don't want to utilize objects that might respond with actual data, we use stubs instead. The lightest and most static kind of test double is known as a stub.

Use Cases

• We can implement an interface that can separate us from the third-party library if we are developing the back end of a small application that will interact with an API. That interface will eventually produce hard-coded values and serve as a stub. In conclusion, unit tests can make use of values.
• If we are testing a single application, we will put in place a stub for the Rest APIs that it is based on. We can also make it with the aid of any internal tool created by the development team.

What is Mock?

A mock is like a stand-in actor who not only says the lines but also pretends to be the real thing, reacting in certain ways. In programming, a mock can do more than a stub. It can mimic how the real part of the program behaves and even check if certain actions happened. We use mocks when we want to test interactions between different parts of the program.

The objects that hold method calls are mocks. The dynamic wrappers for dependencies utilized in the tests were referred to. It is used to document and validate how the Java classes interact with one another. The most potent and adaptable variation of the test doubles is known as a mock. We employ a technique called mocking (). Mocks and stubs are identical, however, you may assert against a mock object whereas you can't with a stub. A mock object decides whether the unit test has passed or failed. There’s usually no more than one mock per test.

Uses Cases of Mock

• A Mockito framework can be used to mock the dependent classes if the back end of an application that is being developed has a lot of classes that need to be tested.
• A mock framework like mountebank or WireMock can be used if we need to detach from the API requirements in HTTP while constructing an application's back end. Then make a fake for the test's dependency classes.

Stub vs Mock

Below are the differences between stub and mock: 

Conclusion

In conclusion, understanding the difference between Mocks and Stubs is crucial for effective testing. Mocks are ideal for verifying interactions between objects, while Stubs are better suited for providing controlled responses during tests. Choosing the right tool Mocks vs. Stubs ensures that your tests are both accurate and maintainable, leading to more reliable software development.