Testing Complex Logic Within Task Runners in Java

In this blog post, we’ll explore a common challenge faced by Java developers - testing complex logic within task runners. We’ll discuss a practical approach to isolate and test the logic within task runners effectively.

The Challenge

Consider a scenario where you have a codebase structured with a TaskRunner-like pattern, encapsulating various tasks. For instance:

class Measurer {
    public <T> T performanceMeasurerTaskRunner(Supplier<T> supplier) {
        long startTime = System.currentTimeMillis();
        
        T res = supplier.get();
        
        long endTime = System.currentTimeMillis();
        long runningTime = endTime - startTime;
        System.out.println("Task performed in " + runningTime + " milliseconds");

        return res;
    }
}

Now, let’s say you want to test the logic within the usefulTask function without being encumbered by the performance measurement code. We’ll explore a solution that allows us to isolate and test usefulTask independently.

The Solution

To address this issue, we can mock the Measurer class, particularly the performanceMeasurerTaskRunner method, so that it bypasses the performance measurement logic. Here’s how you can do it:

@Mock
private Measurer mockedMeasurer;

@InjectMocks
private MainClass mainClass;

private void mockTaskRunnerWithPassThrough() {
    when(mockedMeasurer.performanceMeasurerTaskRunner(any(Supplier.class))).thenAnswer(invocation -> {
        Supplier<?> supplier = invocation.getArgument(0);
        return supplier.get();
    });
}

@Test
void testUsefulTask() {
    mockTaskRunnerWithPassThrough();
    mainClass.usefulJob();
}

In the code above, we configure the mockedMeasurer to pass through any calls to its underlying Supplier.

Benefits of the Approach

Isolation: This approach allows us to isolate and test specific logic within the task runner, ignoring unrelated complexities.

Simplicity: It simplifies the testing process, especially when dealing with complex dependencies such as databases or external APIs.

Conclusion

Testing complex logic within task runners in Java can be challenging, but by employing this technique, you can focus your testing efforts on the specific logic you need to validate. This method provides flexibility and maintainability, ensuring your tests remain concise and targeted, even in complex codebases.

In conclusion, while it’s ideal to separate logic into independent functions for testing, this approach offers a practical solution for scenarios where such separation is not feasible. By understanding and utilizing the power of mocking, you can streamline your testing process and maintain code quality effectively.

We encourage you to apply these techniques in your Java projects and share your experiences in the comments section below. If you have any questions or need further clarification, feel free to ask.