PIT vs pymute

PIT is a free mutation-testing tool for Java and JVM bytecode projects. It measures whether unit tests detect faults by running them against modified versions of application code. Configurable bytecode mutations can remove method calls, invert logic, or change return values. PIT selects and prioritizes tests using line coverage, execution speed, and naming conventions, then reports mutation coverage alongside line coverage. It can run from the command line, Ant, or Maven; third-party integrations are listed for Gradle, Eclipse, and IntelliJ. Java is supported directly, and Kotlin use is available through the ArcMutate plugin. PIT supports JUnit 3, JUnit 4, and TestNG; JUnit 5 needs a plugin. Versions 1.4.0 and later require Java 8 or above and JUnit or TestNG on the classpath. Mutation runs can take a long time depending on codebase size and test-suite speed, so PIT recommends focusing on changed code. It mutates bytecode and requires line numbers and source file names in that bytecode.

pymute is a free mutation testing tool for Python projects using pytest or tox, written in Rust. It creates a temporary directory for each mutant and changes Python file text rather than operating on the abstract syntax tree. Pytest is the default runner, and documented mutation types include math operators, conjunctions, booleans, control flow, comparisons and numbers. By default, it reports mutants that survive because tests pass; other output levels can show caught mutants or process output. Options let users filter modules with a glob, select tests and mutation types, set thread count and cap the number of mutants. That cap runs a randomly selected subset. Installation uses Cargo from crates.io or GitHub and requires Rust and Cargo. With pytest, tests need to run from the project root in independent copies and exercise the local copy rather than an installed package. Tox sets up a separate environment and installs the package for each mutant, which the project describes as considerably slower. Parallel threads each need temporary disk space, and a run may fail if /tmp runs out. The repository identifies its license as Unlicense.