# Mutation testing metrics (Scala)

Zero-dependency library to calculate mutation testing metrics in Scala.

See mutant states and metrics in the Stryker handbook for more details about mutation testing metrics.

Cross-compiled for Scala 2.12, 2.13, Dotty, Scala.js 0.6.x and Scala Native 0.3.x.

## Usage example

Add the dependency to your project :

    libraryDependencies += "io.stryker-mutator" %% "mutation-testing-metrics" % version

If you use Scala.js or Scala Native, use `%%%` instead after the groupId.

First create the mutation test report:

    import mutationtesting._
    val report = MutationTestReport(thresholds = Thresholds(high = 80, low = 10),
      files = Map(
        "src/stryker4s/Stryker4s.scala" -> MutationTestResult(
          source = "case class Stryker4s(foo: String)",
          mutants = Seq(
            MutantResult("1", "BinaryOperator", "-", Location(Position(1, 2), Position(2, 3)), status = MutantStatus.Killed)
          )
        )
      )
    )

The `MutationTestReport` case classes generate a JSON compliant with the mutation-testing JSON schema.

Then calculate and use metrics from that report:

    val metrics: MetricsResult = Metrics.calculateMetrics(report)

That report will have all the metrics you need:

    val mutationScore = metrics.mutationScore
    // mutationScore: Double = 70.12987012987013
    val killed = metrics.killed
    // killed: Int = 162
    val survived = metrics.survived
    // survived: Int = 69

## mutation-testing-metrics-circe

Circe transcodings are provided by the `mutation-testing-metrics-circe` library to work with JSON if you don't want the extra dependency on `circe-generic`. It has two dependencies: `circe-core` and `circe-parser`.

    libraryDependencies += "io.stryker-mutator" %% "mutation-testing-metrics-circe" % version

### Encoding

Import the encoder:

    import io.circe.syntax._
    import mutationtesting.MutationReportEncoder._

    val encoded = report.asJson

### Decoding

Import the decoder:

    import io.circe.parser.decode
    import mutationtesting.MutationReportDecoder._

    val decoded = decode[MutationTestReport](json)

## API reference

### `MetricsResult`

A `MetricsResult` has the following properties, as described in the handbook:

    metrics.killed
    // res1: Int = 162
    metrics.survived
    // res2: Int = 69
    metrics.timeout
    // res3: Int = 0
    metrics.noCoverage
    // res4: Int = 0
    metrics.compileErrors
    // res5: Int = 0
    metrics.totalDetected
    // res6: Int = 162
    metrics.totalUndetected
    // res7: Int = 69
    metrics.totalCovered
    // res8: Int = 231
    metrics.totalValid
    // res9: Int = 231
    metrics.totalInvalid
    // res10: Int = 0
    metrics.totalMutants
    // res11: Int = 231
    metrics.mutationScore
    // res12: Double = 70.12987012987013
    metrics.mutationScoreBasedOnCoveredCode
    // res13: Double = 70.12987012987013

- `MetricsResult` is a trait with three implementations:
  - `MetricsResultRoot`: The root of a `MetricsResult`, contains zero or more `MetricsResult`'s
  - `MetricsDirectory`: Representation of a directory. Has a directory name and zero or more `MetricsResult`'s
  - `MetricsFile`: Representation of a file with mutated code. Has a filename and zero or more `MetricMutant`'s
- `MetricMutant`: Contains a `MutantStatus`

## Contributing

To use this project, you will need sbt. The recommended way on macOS/Linux is with sbt-extras. On Windows, you can install sbt using the official .msi.

This project uses the sbt-crossproject plugin for multiple build targets. You can compile code with `sbt compile` and run tests with `sbt test`. Running `sbt +test` will compile and test all targets.

In CI, JS and Native will only be compiled, while tests are run on the JVM project to provide faster CI builds. Publishing is done on all targets. For more information on cross-compilation in sbt, see https://www.scala-sbt.org/1.x/docs/Cross-Build.html.

This readme uses mdoc. To edit it, please edit the readme in docs and call `sbt docs/mdoc` to compile the readme in the root of the project.