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Coverlet as a 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

Usage: coverlet [arguments] [options]

  <ASSEMBLY>  Path to the test assembly.

  -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
  -v|--verbosity           Sets the verbosity level of the command. Allowed values are quiet, minimal, normal, detailed.
  -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.
  --threshold-stat         Coverage statistic used to enforce the threshold value.
  --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.
  --exclude-by-attribute   Attributes to exclude from code coverage.
  --include-test-assembly  Specifies whether to report code coverage of the test assembly.
  --single-hit             Specifies whether to limit code coverage hit reporting to a single hit for each location.
  --merge-with             Path to existing coverage result to merge.
  --use-source-link        Specifies whether to use SourceLink URIs in place of file system paths.

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
CodeCoverageB Branch-level code coverage
CodeCoverageM Method-level code coverage
CodeCoverageAbsLTotal The total number of lines
CodeCoverageAbsLCovered The number of covered lines
CodeCoverageAbsBTotal The total number of branches
CodeCoverageAbsBCovered The number of covered branches
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.


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

By default, Coverlet will validate the threshold value against the coverage result of each module. The --threshold-stat option allows you to change this behaviour and can have any of the following values:

  • Minimum (Default): Ensures the coverage result of each module isn't less than the threshold
  • Total: Ensures the total combined coverage result of all modules isn't less than the threshold
  • Average: Ensures the average coverage result of all modules isn't less than the threshold

The following command will compare the threshold value with the overall total coverage of all modules:

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

Excluding From Coverage


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"


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

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


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


  • --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.


  • --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.

You can also include coverage of the test assembly itself by specifying the --include-test-assembly flag.

Exit Codes

Coverlet outputs specific exit codes to better support build automation systems for determining failures and take action on it.

0 - Success.
1 - If any test fails.
2 - Coverage percentage is below threshold.
3 - Test fails and also coverage percentage is below threshold.
101 - General exception occured during coverlet process.
102 - Missing options or invalid arguments for coverlet process.
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