How to Unit-Test Methods without Parameters in Java

Learn how to effectively unit-test methods without parameters using Java. Discover techniques for passing values during testing and best practices for mocking.
---
This video is based on the question https://stackoverflow.com/q/72292368/ asked by the user 'Mate25' ( https://stackoverflow.com/u/17002231/ ) and on the answer https://stackoverflow.com/a/72292680/ provided by the user 'Ryan' ( https://stackoverflow.com/u/11385052/ ) 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: How can I pass value to a method which doesnt have parameters?

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.
---
How to Unit-Test Methods without Parameters in Java

Unit testing is a vital part of software development, ensuring that individual components of your code work as expected. However, it can become challenging when trying to test a method that doesn't take any parameters. In this post, we'll explore a common scenario in Java where you might want to pass values to a method that doesn't accept any parameters, particularly focusing on methods that gather input from the user.

The Problem: Methods without Parameters

Imagine you have a Java method meant to authenticate a user, which looks like this:

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

The challenge arises when you want to unit-test this method. Since it relies on Scanner to read input from the console, it makes it difficult to pass values while running tests. The goal is to verify that the authenticateUser method can create a User object based on provided credentials without having to interact with the console input.

The Solution: Simulating Input

To effectively unit-test a method without parameters, you can simulate the user input using InputStream. Here’s a breakdown of how to achieve that.

Step-by-Step Implementation

Create Test Input: You will create a string that mimics the user input. In this case, it will contain the username and password separated by new lines.

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

Redirect System Input: Before invoking the method you want to test, you need to redirect System.in to your simulated input. This allows the method to read from your string instead of waiting for console input.

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

Call the Method: Now you can call your authenticateUser method, which will use the simulated input.

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

Restore Original Input: Don't forget to restore the original input stream after you've called your method to prevent side effects on other tests.

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

Example Code

Here’s how the complete test might look:

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

Summary

In Java, testing methods that do not accept parameters can be efficiently accomplished by redirecting the System.in stream to simulate user input. By following the outlined steps, you can ensure that your tests validate the functionality of methods like authenticateUser. This method of testing not only helps maintain the integrity of your code but also boosts confidence in your application’s behavior.

Now, you can confidently unit-test methods without parameters, and harness the power of mock objects effectively in your tests!