Mutation testing is a process to verify the correctness of our tests. It adds a new metric, "mutation coverage", that complements the line coverage to improve our software.

1. Mutation testing
Raúl Ávila

2. I want you to
increase the test
coverage of our
legacy systems
from 0% to more
than 50%…no
matter how!
OK!

3. Test Coverage = 100%

4. Is there any other (automatic) way
to measure the quality of our tests?
Mutation Testing!

5. Mutation testing: process
1. Modify production code
• Modifications are called mutations
2. After each mutation -> Run test suite
3. If the suite passes -> Mutation has survived
4. If the suite fails -> Mutation killed!
New metric: mutation coverage

6. Mutation testing in Java
Integration with Maven

7. Example 1

8. Example 1: missing assertions

9. Example 2

10. Example 2

11. Example 2: insufficient test cases

12. Example 2: insufficient test cases

13. Examples 3

14. Examples 3

15. Examples 3: verify interactions

16. Thank you
https://github.com/raulavila/pit-example