Stub Vs Mock: Choosing the Right Test Double

When it’s about unit testing in software development, one must know the key difference between Mocks and Stubs to ensure effective test coverage. Both of them are important tools and are used to simulate the behavior of dependencies in your code. However, they serve different purposes. Businesses must know Mocks vs Stubs and when to use either of these to create more reliable and maintainable tests, resulting in improved software.

In this article, we’ll discuss the comparison between stub vs mock and which one you should choose.

What Are Test Doubles: Stub vs Mock?

Test doubles play an important role in software testing. They are stand-ins for real objects, letting us isolate specific parts of our code and test them in isolation. It’s like having a substitute teacher for your code, but it’s only more hilarious. Though there are numerous kinds of test doubles, the most common include stubs and mocks and both play an important role in behavior verification and state verification during unit testing.

These test doubles are used to simulate the behavior/state of real objects or components that are external to the unit being tested. Mocks and stubs play vital roles in the software testing process, letting developers verify behavior and ensure the correctness of their code.

What is Stub?

A stub is the simplest part of the program that gives a basic response. Testers use stubs when they want to test something without needing the real part that does the work. The objects known as “stubs” store specified data and use it while generating replies for tests.

In simpler words, a stub is an object that looks like a genuine object but only has the ways required for testing. When we don’t want to use objects that might respond with actual data, stubs are rather used. The lightest and most static kind of test double is referred to as a stub.

What is Mock?

Mock is the vigilant guardian of interaction testing. A mock object is an object that accurately records method calls and takes pride in asserting whether expected interactions took place or not. Mocks are suitable when your mission is to test the interactions between the real object being under test and its collaborators.

Mocks are the go-to choice to ensure that your code collaborates with other components as required. For example, imagine testing an email service whose purpose is to send a confirmation message after a successful purchase. With a mock, you can verify that the expected communication occurred.

The Key Differences between Mocks and Stubs

When it comes to creating effective unit tests, one must understand the differences between mocks and stubs. Though both are test doubles that simulate the behavior or state of real objects or components, they have unique characteristics that make them ideal for different testing scenarios.

Implementation and Dependency Verification

One of the main differences between mocks and stubs is its implementation and dependency verification. Mocks are useful in verifying the right interaction between objects by simulating the behavior and dependencies’ expectations. They set up predefined expectations and let us verify if the interactions occur as expected.

While, stubs provide predetermined responses to particular method calls, allowing you to control the output of the tested unit.

Simulating Real-World Scenarios

Mocks and stubs are different in terms of their ability to simulate real-world scenarios. Though mocks focus on behavior verification, stubs give preference to state verification.

With mocks, you can verify whether specific interactions have occurred or not, while stubs let you test specific outcomes based on pre-defined responses.

Test Complexity and Object Dependencies

Another notable difference between mocks and stubs is their use in testing complex units and handling object dependencies. Mocks are mostly used in more complex test cases involving multiple dependencies and interactions. However, stubs are simple and used in the case of minimal dependencies.

Stub vs Mock: Key Differences

Mentioned below are the key differences between stub and mock: 

Parameters	Stub	Mock
Data Source	Stubs’ data source is hard coded. It is frequently closely connected to the test suite.	A mock behaves like the real objects that code depends on.
Purpose	The main focus of stub is state verification.	While the mock’ purpose is characteristic verification.
Created by	Most stubs are handwritten, but others are designed using tools.	Mocks are usually third-party libraries.
Use	It is mostly used for straightforward test suites.	Large test suites are often where mocks are employed.
Graphics User Interface/User Interface	Stubs do not have a GUI.	Mocks have a GUI.
Benefits	Stub has vast free tools and a wealth of online resources which can be accessed anytime.	One can access open-source tools and internet resources.
Drawbacks	Since the data is hard-coded, test cases pair closely.	Used mainly by the developers rather than testers.
Technical Knowledge	One must have basic knowledge to use stubs.	To use mocks, one must have adequate technical knowledge.
Used By	Stubs are used by developers, testers, or are produced by tools.	Developers deploy mocks using third-party libraries

 

In the end, knowing the difference between stub vs mock is important for effective testing. Mocks are used to verify interactions between objects, while Stubs are ideal for offering controlled responses during tests. Choosing the right tool Mocks vs. Stubs ensures that your tests are both accurate and maintainable, leading to more reliable application development.

If you want custom software for your business and want to choose the most suitable test double that can accurately test your software and identify any potential issues or bugs, then connect with Kodehash Technologies. Our expertly designed test strategies help identify and resolve potential issues at the earliest.

Connect with us today, and let us help you design robust, reliable software with the right testing strategies.

Stub vs Mock: FAQ

Mention the difference related to stub vs mock?

Stubs provide predefined responses to calls and focus on outcomes. On the other hand, mocks record and validate interactions between the actual database objects, thus focusing on behavior.

Is it possible to use both stubs and mocks in one test?

Yes, combining stubs and mocks is possible, based on the scenario. However, give importance to readability and maintainability to create a coherent test structure.