Mutation testing involves modifying a program in small ways.

Each mutated version is called a mutant and tests detect and reject mutants by causing the behavior of the original version to differ from the mutant. This is called killing the mutant.

The goals of mutation testing are multiple:

• identify weakly tested pieces of code (those for which mutants are not killed)
• identify weak tests (those that never kill mutants)
• compute the mutation score, the mutation score is the number of mutants killed / total number of mutants.
• learn about error propagation and state infection in the program

Python

• Mutatest
• Mutpy

C#, Scala, Javascript

• Stryker