coverlet

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

Installation

Global Tool:

dotnet tool install --global coverlet.console

Package Reference:

dotnet add package coverlet.msbuild

How It Works

Coverlet generates code coverage information by going 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 can be used either as a .NET Core global tool that can be invoked from a terminal or as a NuGet package that integrates with the MSBuild system of your test project.

Global Tool

To see a list of options, run:

coverlet --help

The current options are (output of coverlet --help):

Cross platform .NET Core code coverage tool 1.0.0.0

Usage: coverlet [arguments] [options]

Arguments:
  <ASSEMBLY>  Path to the test assembly.

Options:
  -h|--help               Show help information
  -v|--version            Show version information
  -t|--target             Path to the test runner application.
  -a|--targetargs         Arguments to be passed to the test runner.
  -o|--output             Output of the generated coverage report
  -f|--format             Format of the generated coverage report.
  --threshold             Exits with error if the coverage % is below value.
  --threshold-type        Coverage type to apply the threshold to.
  --exclude               Filter expressions to exclude specific modules and types.
  --include               Filter expressions to include specific modules and types.
  --include-directory     Include directories containing additional assemblies to be instrumented.
  --exclude-by-file       Glob patterns specifying source files to exclude.
  --include-directory     Include directories containing additional assemblies to be instrumented.
  --exclude-by-attribute  Attributes to exclude from code coverage.
  --merge-with            Path to existing coverage result to merge.

Code Coverage

The coverlet tool is invoked by specifying the path to the assembly that contains the unit tests. You also need to specify the test runner and the arguments to pass to the test runner using the --target and --targetargs options respectively. The invocation of the test runner with the supplied arguments must not involve a recompilation of the unit test assembly or no coverage data will be generated.

The following example shows how to use the familiar dotnet test toolchain:

coverlet /path/to/test-assembly.dll --target "dotnet" --targetargs "test /path/to/test-project --no-build"

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

Note: The --no-build flag is specified so that the /path/to/test-assembly.dll isn't rebuilt

Coverage Output

Coverlet can generate coverage results in multiple formats, which is specified using the --format or -f options. For example, the following command emits coverage results in the opencover format instead of json:

coverlet <ASSEMBLY> --target <TARGET> --targetargs <TARGETARGS> --format opencover

Supported Formats:

• json (default)
• lcov
• opencover
• cobertura
• teamcity

The --format option can be specified multiple times to output multiple formats in a single run:

coverlet <ASSEMBLY> --target <TARGET> --targetargs <TARGETARGS> --format opencover --format lcov

By default, Coverlet will output the coverage results file(s) in the current working directory. The --output or -o options can be used to override this behaviour.

coverlet <ASSEMBLY> --target <TARGET> --targetargs <TARGETARGS> --output "/custom/path/result.json"

The above command will write the results to the supplied path, if no file extension is specified it'll use the standard extension of the selected output format. To specify a directory instead, simply append a / to the end of the value.

coverlet <ASSEMBLY> --target <TARGET> --targetargs <TARGETARGS> --output "/custom/directory/" -f json -f lcov

TeamCity Output

Coverlet can output basic code coverage statistics using TeamCity service messages.

coverlet <ASSEMBLY> --target <TARGET> --targetargs <TARGETARGS> --output teamcity

The currently supported TeamCity statistics are:

TeamCity Statistic Key	Description
CodeCoverageL	Line-level code coverage
CodeCoverageC	Class-level code coverage
CodeCoverageM	Method-level code coverage
CodeCoverageAbsLTotal	The total number of lines
CodeCoverageAbsLCovered	The number of covered lines
CodeCoverageAbsCTotal	The total number of classes
CodeCoverageAbsCCovered	The number of covered classes
CodeCoverageAbsMTotal	The total number of methods
CodeCoverageAbsMCovered	The number of covered methods

Merging Results

With Coverlet you can combine the output of multiple coverage runs into a single result.

coverlet <ASSEMBLY> --target <TARGET> --targetargs <TARGETARGS> --merge-with "/path/to/result.json" --format opencover

The value given to --merge-with must be a path to Coverlet's own json result format.

Threshold

Coverlet allows you to specify a coverage threshold below which it returns a non-zero exit code. This allows you to enforce a minimum coverage percent on all changes to your project.

coverlet <ASSEMBLY> --target <TARGET> --targetargs <TARGETARGS> --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 --threshold-type option. For example to apply the threshold check to only line coverage:

coverlet <ASSEMBLY> --target <TARGET> --targetargs <TARGETARGS> --threshold 80 --threshold-type line

You can specify the --threshold-type option multiple times. Valid values include line, branch and method.

coverlet <ASSEMBLY> --target <TARGET> --targetargs <TARGETARGS> --threshold 80 --threshold-type line --threshold-type method

Excluding From Coverage

Attributes

You can ignore a method or an entire class from code coverage by creating and applying the ExcludeFromCodeCoverage attribute present in the System.Diagnostics.CodeAnalysis namespace.

You can also ignore additional attributes by using the ExcludeByAttribute property (short name or full name supported):

coverlet <ASSEMBLY> --target <TARGET> --targetargs <TARGETARGS> --exclude-by-attribute "Obsolete,GeneratedCodeAttribute,CompilerGeneratedAttribute"

Source Files

You can also ignore specific source files from code coverage using the --exclude-by-file option

• Can be specified multiple times
• Use absolute or relative paths (relative to the project directory)
• Use file path or directory path with globbing (e.g dir1/*.cs)

coverlet <ASSEMBLY> --target <TARGET> --targetargs <TARGETARGS> --exclude-by-file "../dir1/class1.cs"

Filters

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

Syntax: --exclude '[Assembly-Filter]Type-Filter'

Wildcards

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

Examples

• --exclude "[*]*" => Excludes all types in all assemblies (nothing is instrumented)
• --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)
• --exclude "[*]Coverlet.Core.Instrumentation.*" => Excludes all types belonging to Coverlet.Core.Instrumentation namespace in any assembly
• --exclude "[coverlet.*.tests?]*" => Excludes all types in any assembly starting with coverlet. and ending with .test or .tests (the ? makes the s optional)
• --exclude "[coverlet.*]*" --exclude "[*]Coverlet.Core*" => Excludes assemblies matching coverlet.* and excludes all types belonging to the Coverlet.Core namespace in any assembly

coverlet <ASSEMBLY> --target <TARGET> --targetargs <TARGETARGS> --exclude "[coverlet.*]Coverlet.Core.Coverage"

Coverlet goes a step in the other direction by also letting you explicitly set what can be included using the --include option.

Examples

• --include "[*]*" => Includes all types in all assemblies (everything is instrumented)
• --include "[coverlet.*]Coverlet.Core.Coverage" => Includes the Coverage class in the Coverlet.Core namespace belonging to any assembly that matches coverlet.* (e.g coverlet.core)
• --include "[coverlet.*.tests?]*" => Includes all types in any assembly starting with coverlet. and ending with .test or .tests (the ? makes the s optional)

Both --exclude and --include options can be used together but --exclude takes precedence. You can specify the --exclude and --include options multiple times to allow for multiple filter expressions.

MSBuild

In this mode, 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.

If a property takes multiple comma-separated values please note that you will have to add escaped quotes around the string like this: /p:Exclude=\"[coverlet.*]*,[*]Coverlet.Core*\", /p:Include=\"[coverlet.*]*,[*]Coverlet.Core*\", or /p:CoverletOutputFormat=\"json,opencover\".

Note for Powershell / VSTS users

To exclude or include multiple assemblies when using Powershell scripts or creating a .yaml file for a VSTS build %2c should be used as a separator. Msbuild will translate this symbol to ,.

/p:Exclude="[*]*Examples?%2c[*]*Startup"

VSTS builds do not require double quotes to be unescaped:

dotnet test --configuration $(buildConfiguration) --no-build /p:CollectCoverage=true /p:CoverletOutputFormat=cobertura /p:CoverletOutput=$(Build.SourcesDirectory)/TestResults/Coverage/ /p:Exclude="[MyAppName.DebugHost]*%2c[MyAppNamet.WebHost]*%2c[MyAppName.App]*"

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
• teamcity

You can specify multiple output formats by separating them with a comma (,).

The output of the coverage result can be specified using the CoverletOutput property.

dotnet test /p:CollectCoverage=true /p:CoverletOutput='./result.json'

To specify a directory where all results will be written to (especially if using multiple formats), end the value with a /.

dotnet test /p:CollectCoverage=true /p:CoverletOutput='./results/'

Merging Results

With Coverlet you can combine the output of multiple coverage runs into a single result.

dotnet test /p:CollectCoverage=true /p:MergeWith='/path/to/result.json'

The value given to /p:MergeWith must be a path to Coverlet's own json result format.

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 the ExcludeFromCodeCoverage attribute present in the System.Diagnostics.CodeAnalysis namespace.

You can also ignore additional attributes by using the ExcludeByAttribute property (short name or full name supported):

dotnet test /p:CollectCoverage=true /p:ExcludeByAttribute="Obsolete,GeneratedCodeAttribute,CompilerGeneratedAttribute"

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"

Coverlet goes a step in the other direction by also letting you explicitly set what can be included using the Include property.

Examples

• /p:Include="[*]*" => Includes all types in all assemblies (everything is instrumented)
• /p:Include="[coverlet.*]Coverlet.Core.Coverage" => Includes the Coverage class in the Coverlet.Core namespace belonging to any assembly that matches coverlet.* (e.g coverlet.core)
• /p:Include="[coverlet.*.tests?]*" => Includes all types in any assembly starting with coverlet. and ending with .test or .tests (the ? makes the s optional)

Both Exclude and Include properties can be used together but Exclude takes precedence.

You can specify multiple filter expressions by separting them with a comma (,).

Cake Addin

If you're using Cake Build for your build script you can use the Cake.Coverlet addin to provide you extensions to dotnet test for passing coverlet arguments in a strongly typed manner.

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.

Performance testing

There is a performance test for the hit counting instrumentation in the test project coverlet.core.performancetest. Build the project with the msbuild step above and then run:

dotnet test /p:CollectCoverage=true test/coverlet.core.performancetest/

The duration of the test can be tweaked by changing the number of iterations in the [InlineData] in the PerformanceTest class.

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.