coverlet

Coverlet is a cross platform code coverage library for .NET Core, with support for line, branch and method coverage.

Installation

Available on NuGet

Visual Studio:

PM> Install-Package coverlet.msbuild

.NET Core CLI:

dotnet add package coverlet.msbuild

How It Works

Coverlet integrates with the MSBuild system and that allows it to go through the following process:

Before Tests Run

Locates the unit test assembly and selects all the referenced assemblies that have PDBs.
Instruments the selected assemblies by inserting code to record sequence point hits to a temporary file.

After Tests Run

Restore the original non-instrumented assembly files.
Read the recorded hits information from the temporary file.
Generate the coverage result from the hits information and write it to a file.

Note: The assembly you'd like to get coverage for must be different from the assembly that contains the tests

Usage

Coverlet doesn't require any additional setup other than including the NuGet package in the unit test project. It integrates with the dotnet test infrastructure built into the .NET Core CLI and when enabled, will automatically generate coverage results after tests are run.

Code Coverage

Enabling code coverage is as simple as setting the CollectCoverage property to true

dotnet test /p:CollectCoverage=true

After the above command is run, a coverage.json file containing the results will be generated in the root directory of the test project. A summary of the results will also be displayed in the terminal.

Coverage Output

Coverlet can generate coverage results in multiple formats, which is specified using the CoverletOutputFormat property. For example, the following command emits coverage results in the opencover format:

dotnet test /p:CollectCoverage=true /p:CoverletOutputFormat=opencover

Supported Formats:

json (default)
lcov
opencover
cobertura

The output folder of the coverage result file can also be specified using the CoverletOutputDirectory property.

Threshold

Coverlet allows you to specify a coverage threshold below which it fails the build. This allows you to enforce a minimum coverage percent on all changes to your project.

dotnet test /p:CollectCoverage=true /p:Threshold=80

The above command will automatically fail the build if the line, branch or method coverage of any of the instrumented modules falls below 80%. You can specify what type of coverage to apply the threshold value to using the ThresholdType property. For example to apply the threshold check to only line coverage:

dotnet test /p:CollectCoverage=true /p:Threshold=80 /p:ThresholdType=line

You can specify multiple values for ThresholdType by separating them with commas. Valid values include line, branch and method.

Excluding From Coverage

Attributes

You can ignore a method or an entire class from code coverage by creating and applying any of the following attributes:

ExcludeFromCoverage
ExcludeFromCoverageAttribute

Coverlet just uses the type name, so the attributes can be created under any namespace of your choosing.

Source Files

You can also ignore specific source files from code coverage using the ExcludeByFile property

Use single or multiple paths (separate by comma)
Use absolute or relative paths (relative to the project directory)
Use file path or directory path with globbing (e.g dir1/*.cs)

dotnet test /p:CollectCoverage=true /p:ExcludeByFile=\"../dir1/class1.cs,../dir2/*.cs,../dir3/**/*.cs,\"

Filters

Coverlet gives the ability to have fine grained control over what gets excluded using "filter expressions".

Syntax: /p:Exclude=[Assembly-Filter]Type-Filter

Wildcards

* => matches zero or more characters
? => the prefixed character is optional

Examples

/p:Exclude="[*]*" => Excludes all types in all assemblies (nothing is instrumented)
/p:Exclude="[coverlet.*]Coverlet.Core.Coverage" => Excludes the Coverage class in the Coverlet.Core namespace belonging to any assembly that matches coverlet.* (e.g coverlet.core)
/p:Exclude="[*]Coverlet.Core.Instrumentation.*" => Excludes all types belonging to Coverlet.Core.Instrumentation namespace in any assembly
/p:Exclude="[coverlet.*.tests?]*" => Excludes all types in any assembly starting with coverlet. and ending with .test or .tests (the ? makes the s optional)
/p:Exclude=\"[coverlet.*]*,[*]Coverlet.Core*\" => Excludes assemblies matching coverlet.* and excludes all types belonging to the Coverlet.Core namespace in any assembly

dotnet test /p:CollectCoverage=true /p:Exclude="[coverlet.*]Coverlet.Core.Coverage"

You can specify multiple filter expressions by separting them with a comma (,). If you specify multiple filters, then you'll have to escape the surrounding quotes like this: /p:Exclude=\"[coverlet.*]*,[*]Coverlet.Core*\".

Roadmap

Merging outputs (multiple test projects, one coverage result)
Support for more output formats (e.g. JaCoCo)
Console runner (removes the need for requiring a NuGet package)

Issues & Contributions

If you find a bug or have a feature request, please report them at this repository's issues section. Contributions are highly welcome, however, except for very small changes, kindly file an issue and let's have a discussion before you open a pull request.

Building The Project

Clone this repo:

git clone https://github.com/tonerdo/coverlet

Change directory to repo root:

cd coverlet

Execute build script:

dotnet msbuild build.proj

This will result in the following:

Restore all NuGet packages required for building
Build and publish all projects. Final binaries are placed into <repo_root>\build\<Configuration>
Build and run tests

These steps must be followed before you attempt to open the solution in an IDE (e.g. Visual Studio, Rider) for all projects to be loaded successfully.

Code of Conduct

This project enforces a code of conduct in line with the contributor covenant. See CODE OF CONDUCT for details.

License

This project is licensed under the MIT license. See the LICENSE file for more info.

csMACnz/coverlet