Скачать или смотреть Mastering Unit Testing for a Random Number Generator in Java

Discover how to effectively unit test a `random number generator` in Java using JUnit, including practical examples and best practices.
---
This video is based on the question https://stackoverflow.com/q/71188966/ asked by the user 'JCS' ( https://stackoverflow.com/u/12723802/ ) and on the answer https://stackoverflow.com/a/71189012/ provided by the user 'Győző Nyári' ( https://stackoverflow.com/u/4419808/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Unit Testing for a random number

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Mastering Unit Testing for a Random Number Generator in Java

Unit testing is an essential practice in software development. It ensures that individual parts of your code work as expected. One common challenge developers face is testing components that involve randomness, such as a random number generator. In this guide, we'll tackle this problem by leveraging JUnit for effective testing.

The Problem: Testing a Random Number Generator

Imagine you’re developing a simple game that uses a dice roll generator. The code for generating a random number looks something like this:

[[See Video to Reveal this Text or Code Snippet]]

While the DiceRoll() method works fine, testing it directly can be tricky. Since the output is random, writing a unit test that consistently passes can become a challenge. This is where we need to make some strategic changes to our code.

The Solution: Refactoring the Dice Class

To effectively unit test the Dice class, we can refactor it to allow for dependency injection. This method involves passing a Random instance to the Dice class, which enables us to control what the Random instance generates during our tests. Here’s how we can implement this:

Step 1: Modify the Dice Class

Refactor your Dice class as follows:

[[See Video to Reveal this Text or Code Snippet]]

Step 2: Write the Unit Test

Now, let's see how we can write you unit tests using JUnit. The key here is to mock the Random class. You can use a mocking library, like Mockito, to achieve this. Here's an example of how a unit test may look.

[[See Video to Reveal this Text or Code Snippet]]

Explanation of the Test Code

Arrange: We create a mock instance of Random so we can have full control over its behavior during the test.

When: We specify that when nextInt(6) is called on our mockRandom, it should return 4.

Act: We call the DiceRoll() method of the Dice class.

Assert: Finally, we check that the output is what we expect. Since nextInt(6) returns 4, our function should return 5 (4 + 1).

Conclusion

By refactoring the Dice class to allow for dependency injection, we can successfully unit test our random number generator using JUnit and Mockito. This approach not only makes your code easier to test but also more flexible and maintainable.

Unit testing can be challenging when randomness is involved, but with the right strategies in place, you can ensure your code remains robust. Happy coding!