Positive vs Negative Tests

Introduction

A natural inclination when writing test cases is to check that a test case behaves as expected with expected input. This is only one side of the coin when writing a test case. To write a test case that comprehensively checks the behavior of a method, we need to check that a method behaves as expected with unexpected input. A positive case tests whether the code behaves like it should. A negative case tests whether the code does not behave like it shouldn’t. These two terms are very difficult to define and are best demonstrated by example.

Differences between positive and negative tests

The best way to demonstrate this concept is to use an example of a human resources department approving leave applications. Suppose that only the human resource manager may approve leave applications. The positive test would assert that a human resource manager can approve applications. Note how the positive test statement mimics the behavior that is expected. This is why we ...