scalac-scoverage-plugin

scoverage is a free Apache licensed code coverage tool for Scala that offers statement and branch coverage. scoverage is available for sbt, Maven, Mill, and Gradle.

NOTE: That this repository contains the Scala compiler plugin for Code coverage in Scala 2 and other coverage utilities for generating reports. For Scala 3 code coverage the compiler natively produces code coverage output, but the reporting logic utilities are then shared with the Scala 2 code coverage utilities in this repo.

Statement Coverage

In traditional code coverage tools, line coverage has been the main metric. This is fine for languages such as Java which are very verbose and very rarely have more than one statement per line, and more usually have one statement spread across multiple lines.

In powerful, expressive languages like Scala, quite often multiple statements, or even branches are included on a single line, eg a very simple example:

val status = if (Color == Red) Stop else Go

If you had a unit test that ran through the Color Red you would get 100% line coverage yet you only have 50% statement coverage.

Let's expand this example out to be multifacted, albeit somewhat contrived:

val status = if (Color == Red) Stop else if (Sign == Stop) Stop else Go

Now we would get 100% code coverage for passing in the values (Green, SpeedLimit).

That's why in scoverage we focus on statement coverage, and don't even include line coverage as a metric. This is a paradigm shift that we hope will take hold.

Branch Coverage

Branch coverage is very useful to ensure all code paths are covered. Scoverage produces branch coverage metrics as a percentage of the total branches. Symbols that are deemed as branch statements are:

If / else statements
Match statements
Partial function cases
Try / catch / finally clauses

In this screenshot you can see the coverage HTML report that shows one branch of the if statement was not executed during the test run. In addition two of the cases in the partial function were not executed.

How to use

This project is the base library for instrumenting code via a scalac compiler plugin. To use scoverage in your project you will need to use one of the build plugins:

scoverage-maven-plugin
sbt-scoverage
gradle-scoverage
sbt-coveralls
mill-contrib-scoverage
Upload report to Codecov: Example Scala Repository
Upload report to Codacy: Documentation

Scoverage support is available for the following tools:

If you want to write a tool that uses this code coverage library then it is available on maven central. Search for scalac-scoverage-plugin.

Excluding code from coverage stats

You can exclude whole classes or packages by name. Pass a semicolon separated list of regexes to the excludedPackages option.

For example:

-P:scoverage:excludedPackages:.*\.utils\..*;.*\.SomeClass;org\.apache\..*

The regular expressions are matched against the fully qualified class name, and must match the entire string to take effect.

Any matched classes will not be instrumented or included in the coverage report.

You can also exclude files from being considered for instrumentation.

-P:scoverage:excludedFiles:.*\/two\/GoodCoverage;.*\/three\/.*

Note: The .scala file extension needs to be omitted from the filename, if one is given.

Note: These two options only work for Scala2. Right now Scala3 does not support a way to exclude packages or files from being instrumented.

You can also mark sections of code with comments like:

// $COVERAGE-OFF$
...
// $COVERAGE-ON$

Any code between two such comments will not be instrumented or included in the coverage report.

Further details are given in the plugin readme's.

Release History

For a full release history please see the releases page.

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