Mutation Tests - Joseph Yeo - Agile SG 2013

Presented in Agile Singapore 2013 Conference

Transcript

1. Mutation Test Joseph Yao A Way to Learn How Good Your Unit Test is
2. Who I am? n Agile Coach at Odd-e n Father, Husband... n Software Craftsman
4. Mutant
5. Mutation Test Mutant causes any test failed? Killed Mutant Yes Survived Mutant No
7. Expectation of Automated Test Any Possible “Bad” Code Change can be Detected
8. int foo (int x, int y)! {! int z = 0;! if ((x>0) && (y>0)) {! z = x;! }! return z;! } int foo (int x, int y)! {! int z = 0;! if ((x>0) && (y>=0)) {! z = x;! }! return z;! } Unit Tests assertEquals(2, foo(2, 2)) assertEquals(0, foo(2, -1)) assertEquals(0, foo(-1, 2)) To assertEquals(2, foo(2, 2)) assertEquals(0, foo(2, 0)) assertEquals(0, foo(-1, 2))
9. int foo (int x, int y)! {! int z = 0;! if ((x>0) && (y>0)) {! z = x;! }! sideEffect(z);! return z;! } int foo (int x, int y)! {! int z = 0;! if ((x>0) && (y>0)) {! z = x;! }! sideEffect(z);! return z;! } n Either missing a test to prove the removed code is needed n Or the removed code is truly Redundant
11. Three Rules of TDD n You are not allowed to write any production code unless it is to make a failing unit test pass. n You are not allowed to write any more of a unit test than is sufficient to fail; and compilation failures are failures. n You are not allowed to write any more production code than is sufficient to pass the one failing unit test.
13. Survived Mutant
14. Problematic Test
15. Mutants n Conditionals Boundary n Negate Conditionals n Math n Increments n Invert Negatives n Inline Constant n Return Values n Void Method Calls n Non Void Method Calls n Constructor Calls More detail at http://pitest.org/quickstart/mutators/
17. NOT
18. Equivalent Mutant >= >
19. Mutation Test Tool
21. http://crestweb.cs.ucl.ac.uk/resources/ mutation_testing_repository/TR-09-06.pdf
22. Q & A Email: joseph.yao.ruozhou@gmail.com Kata Video: http://tudou.com/home/yaoruozhou Github: https://github.com/JosephYao