Introduction: The Challenge of Untested Code

When working with older systems, you may encounter situations where the code lacks sufficient unit tests. This can create a significant obstacle if you need to make changes or enhancements. Without tests, you cannot verify that modifications won’t break existing functionality. So, how do you tackle the problem of changing untested and untestable code?

In this blog post, we’ll explore the challenges of legacy code and provide you with effective strategies for testing and refactoring it, turning a tricky situation into a manageable task.

Understanding the Problem: Why Is Legacy Code Hard to Test?

Before we dive into solutions, it’s crucial to understand why some code is hard to test:

• High Dependencies: Classes often have numerous interdependencies that complicate setups for unit tests.
• Tightly Coupled Code: Code that doesn’t follow separation of concerns often makes isolating functionality for tests difficult.
• Anti-patterns: Practices that undermine good software design can lead to code that’s resistant to testing.

Solution: Strategies for Testing Untested Code

1. Start with Refactoring

Refactoring frequently can ease the burden of writing tests for code that is difficult to work with. Here’s how:

• Modify Visibility: Change private members to protected. This allows you to create test subclasses that can override methods or fields for testing purposes.

Example

Imagine you have a class that initializes data from a database during the constructor—a scenario making unit tests nearly impossible.

Original Code:

public class MyClass {
    public MyClass() {
        // undesirable DB logic
    }
}

Refactored Code:

public class MyClass {
    public MyClass() {
        loadFromDB();
    }

    protected void loadFromDB() {
        // undesirable DB logic
    }
}

By isolating the DB loading into the loadFromDB method, it becomes easy to override this method in a test scenario.

2. Create Test Wrappers

Once you have refactored the code, you can create test wrappers:

Sample Test Code

Your test code could look something like this:

public class MyClassTest {
    public void testSomething() {
        MyClass myClass = new MyClassWrapper();
        // assert logic here
    }

    private static class MyClassWrapper extends MyClass {
        @Override
        protected void loadFromDB() {
            // some mock logic for testing
        }
    }
}

The wrapper allows you to insert mock logic, effectively isolating the test from the actual database dependency.

3. Consider Existing Tools

While these strategies can be quite effective, don’t forget that modern libraries and tools can facilitate the testing process as well. Using frameworks like DBUnit often simplifies scenarios that involve database operations.

4. Caution with Frameworks

While modifying access levels may offer quick wins for testing, it may also expose internal workings which can be problematic for library or framework authors. Ensure you maintain proper encapsulation and design principles unless absolutely necessary.

Conclusion

Testing and refactoring untested or untestable code can feel daunting, but with strategic modifications and the right tools, you can transform legacy systems into maintainable, test-friendly code. By prioritizing refactoring, creating test wrappers, and leveraging available tools, you can make your life easier as a developer and ensure the resilience of your software.

Key Takeaway

Always strive to create testable units of code while being mindful of the impact of your changes on existing functionality. Happy coding!