Getting Started With Mutation Testing Denis Brumann denis.brumann@sensiolabs.de

Denis Brumann @dbrumann denis.brumann@sensiolabs.de

Mutation testing involves modifying a program in small ways. If mutated program produces failing tests, this is called a killed mutant. If tests are green with mutated code, then we have an escaped mutant.

Installation Phar, Phive, Composer, Git or Homebrew Infection requires a recent version of PHP, and XDebug, phpdbg, or pcov enabled.

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Mutators Boolean Substitution Name Original Mutated TrueValue true false FalseValue - + LogicalAnd && || LogicalOr || &&

Mutators Literal Numbers Name Original Mutated OneZeroInteger 0 1 ZeroOneInteger 1 0 DecrementInteger 7 6 IncrementInteger 7 8

Mutators Binary Arithmetic Name Original Mutated Plus + - Minus - + AssignmentEqual == =

Mutators Exceptions Name Original Mutated Throw_ throw new \Exception new \Exception Finally_ try {} catch {} finally {} try {} catch {}

Mutators Equal or Identical Checks Name Original Mutated EqualIdentical == === NotEqualNotIdentical != !== IdenticalEqual === == NotIdenticalNotEqal !== !=

Profiles { "source": { "directories": [ "src" ] }, "timeout": 10, "logs": { "text": "infection.log" }, "mutators": { "@default": true, "@identical": true, } }

More Demo

Performance Only Changed Files CHANGED_FILES=$(git diff origin/master --diff-filter=AM --name-only | grep src/ | paste -sd "," -); INFECTION_FILTER="--filter=${CHANGED_FILES} --ignore-msi-with-no-mutations"; infection --threads=4 $INFECTION_FILTER

vendor/bin/infection --only-covered Performance Only Covered

Performance Disable Filters { "mutators": { "@default": true, "Plus": false, } }

Summary Cons Pros easy setup false positives mutation shows what to test for "better" coverage slow runs in CI + provides coverage report