Mutation Testing
Oli Wennell
Confidence
More than one pair of eyes...
Static analysis...
...
Automated tests
Can we measure test quality?
Yes
Test coverage metrics
But...
validate: function(password) {
if (password.length > 0 && password.length < 10) {
return true;
}
return false;
}
it('An empty string is not a valid password', function() {
assert.equal(
passwordValidation.validate(""),
false);
});
it('A non-empty string is a valid password', () => {
assert.equal(
passwordValidation.validate("A"),
true);
});
And the test coverage is...
100%!
Remove all assertions?...
100%!
Fettle it
Wouldn't it be nice if...
Mutation Testing
validate: function(password) {
if (password.length > 0 && password.length < 10) {
return true;
}
return false;
}
The original code
validate: function(password) {
if (password.length > 0 && password.length <= 10) {
return true;
}
return false;
}
The mutated version
Still from Them! (1954) - http://www.imdb.com/title/tt0047573/
But...
Time
Support
.NET
...and more
Summary
TL;DR
Slides and example code: oliwennell.github.io/
Stryker: stryker-mutator.github.io
Have a chat:
Twitter: @owennell