Theories in Practice: Easy-to-Write Specifications that Catch Bugs

Automated testing during development helps ensure that software works according to the test suite. Traditional test suites verify a few well-picked scenarios or example inputs. However, such example-based testing does not uncover errors in legal inputs that the test writer overlooked. We propose theory-based testing as an adjunct to example-based testing. A theory generalizes a (possibly infinite) set of example-based tests. A theory is an assertion that should be true for any data, and it can be exercised by human-chosen data or by automatic data generation. A theory is expressed in an ordinary programming language, it is easy for developers to use (often even easier than example-based testing), and it serves as a lightweight form of specification. Six case studies demonstrate the utility of theories that generalize existing tests to prevent bugs, clarify intentions, and reveal design problems.