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Test-Driven Development in Java

Preventing Logic Flaws

Explore how test-driven development (TDD) helps identify and prevent logic flaws in Java code by writing tests before production code. Understand the limitations and costs of manual testing, and discover how automated testing can catch errors early to improve code reliability and speed up debugging.

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Logical errors

The idea of logic errors is perhaps what everybody thinks of first when we talk about testing: did it work right? We can’t disagree here—this is really important. As far as users, revenues, our NPSNet Promoter Score®™, and market growth go, if our code doesn’t work right, it doesn’t sell. It’s that simple.

A logical error in design or code is an error where the provided instructions do not accomplish the intended goal

Understanding the limits of manual testing

We know from bitter experience that the simplest logic flaws are often the easiest to create. The examples that we can all relate to are those one-off errors, that NullPointerException from an uninitialized variable, and that exception thrown by a library that wasn’t in the documentation.

Java
public class ManualTestingExample {
    public static void main(String[] args) {
        String name = null; // Simulate a null reference
        
        try {
            int nameLength = name.length(); // This line will throw a NullPointerException
            System.out.println("Name length: " + nameLength);
        } catch (NullPointerException e) {
            System.err.println("NullPointerException occurred: " + e.getMessage());
        }
    }
}

Code explanation

In the above example, we deliberately set the name variable to null, and then we attempt to ...