Muex

brings AST-level mutation testing to Elixir, evaluating the true strength of test suites by injecting deliberate code mutations.

The Pitch

High line coverage does not guarantee high test quality. Tests can execute every line of code without actually asserting on the correctness of state transformations or boundary conditions.

Muex performs AST-level mutation analysis on Elixir codebases. By swapping operators ( + to - , > to >= ), altering boolean logic, and modifying return values, Muex creates "mutants" and runs your test suite against them. If tests pass, the mutant survived—revealing critical gaps in your assertions.

Why Muex?

AST Mutation Engine

Injects precise syntactic mutations directly into Elixir Abstract Syntax Trees without corrupting files.

Concurrent Mutant Execution

Runs test suites against mutated code paths in parallel to minimize overall run time.

Clear Coverage Reports

Distinguishes killed mutants, surviving mutants, and timeout failures with granular reports.

Customizable Operators

Selectively enable or disable specific mutation rules matching your domain risk profile.

The Tech

Who It's For

• Elixir Teams seeking true confidence in mission-critical applications beyond raw code coverage metrics.
• QA & Security Engineers identifying untested edge cases and weak assertion logic.
• Open-Source Maintainers ensuring pull requests preserve strict domain behavior.

Bottom Line

Catch weak assertions and uncover untested code paths by mutating Elixir ASTs with Muex.