Скачать или смотреть How to Fix the NULL Value Issue When Testing Your Java Classes

Discover how to resolve the `NULL` value problem in your Java unit tests effectively when working with generic abstract classes.
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This video is based on the question https://stackoverflow.com/q/65125069/ asked by the user 'JBallester' ( https://stackoverflow.com/u/4169810/ ) and on the answer https://stackoverflow.com/a/65143869/ provided by the user 'Onkar Vaidya' ( https://stackoverflow.com/u/3454420/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the Issue: Testing a Class from a Generic Abstract Class

When diving into unit testing, Java developers often face various challenges depending on their class structure. In this guide, we're discussing a specific issue encountered while testing a class that extends from a generic abstract class.

The problem arose during a test case for a class DateOfBirth that extends the Value abstract class. Everything appears to be on track until the developer runs their unit test and experiences a NULL value being returned, causing the test to fail. Let’s delve deeper into the reason behind this unexpected behavior and the solution to rectify it.

The Code Structure

To better understand the scenario, let's break down the relevant pieces of code:

The Abstract Class: Value<T>

In Java, having a generic abstract class is quite common. Below is the structure of your Value class:

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

The Derived Class: DateOfBirth

Next, we have the DateOfBirth class extending the Value class:

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

The Unit Test: DateOfBirthUnitTest

The test case to check the value assigned to DateOfBirth is structured as follows:

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

The Problem: Why is the Value NULL?

Upon running the unit test, the method theActual.value() returns NULL, causing the test to fail. The root of this issue lies within a small yet critical typo in the constructor of the Value class.

The Solution: Correcting the Typo

The constructor of the Value class should assign the provided parameter aValue to the class variable value, but currently, it's incorrectly assigning the variable itself. Here’s the original line of code that needs correction:

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

The Correct Implementation

Change the constructor to correctly assign the parameter like this:

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

By making this adjustment, the Value class will store the provided parameter correctly, and when you call theActual.value(), it should return the appropriate LocalDate without returning NULL.

Conclusion

Fixing that simple typo in the constructor resolves the issue of the NULL value being returned during your unit tests. Always check variable assignments closely, especially in constructors, to avoid such pitfalls. With this fix, your unit tests should pass as expected, confirming that your DateOfBirth class behaves correctly.

Feel free to follow along and check your own code structure against these solutions. Happy coding and testing!