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PIT Example

Example of running PIT mutation testing tool using JUnit

Running

This example uses Maven, a project management tool that neatly takes care of dependencies.

To run the mutation tests, execute the following commands

mvn clean install                              #clean and compile
mvn test                                       #run jUnit
mvn org.pitest:pitest-maven:mutationCoverage   #run PIT mutation tests

If Maven is not available on your system, there is a provided ant script.

ant
ant test
ant pit

If you prefer to run PIT directly via the command line, run the following:

java -cp target/classes:target/test-classes:lib/junit-4.10.jar:lib/pitest-0.25-SNAPSHOT.jar \
    org.pitest.mutationtest.MutationCoverageReport \
    --reportDir target/pit-reports \
    --targetClasses pitexample.* \
    --sourceDirs src/main/java,src/test/java

and see the generated report in target/pit-reports.

Examining the output

The example has the following method

public boolean myMethod(int a, boolean flag) {
    if (a > 0) {
        return true;
    }
    if (flag) {
        return true;
    }
    return false;
}

That is tested with the following:

@Test public void testMe() {
  MyClass sut = new MyClass();
  assertTrue(sut.myMethod(1, true));
  assertTrue(sut.myMethod(2, true));
  assertTrue(sut.myMethod(1, false));
  assertTrue(sut.myMethod(2, false));
  assertFalse(sut.myMethod(0, false));
}

The output from PIT indicates that it created 6 mutations, and only killed 5 of them (83%). Looking at the html output, it becomes clear that there is another assertion missing. Adding the following assertion and rerunning will complete the test.

assertTrue(sut.myMethod(0, true));

Integrating with an existing system

It is imperative that you compile all code with debug information. This means that you must add debug="true" to the javac blocks in your ant file.