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.
--exclude-by-file Glob patterns specifying source files to exclude.
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
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
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.
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 theCoverlet.Core
namespace belonging to any assembly that matchescoverlet.*
(e.gcoverlet.core
)--exclude "[*]Coverlet.Core.Instrumentation.*"
=> Excludes all types belonging toCoverlet.Core.Instrumentation
namespace in any assembly--exclude "[coverlet.*.tests?]*"
=> Excludes all types in any assembly starting withcoverlet.
and ending with.test
or.tests
(the?
makes thes
optional)--exclude "[coverlet.*]*" --exclude "[*]Coverlet.Core*"
=> Excludes assemblies matchingcoverlet.*
and excludes all types belonging to theCoverlet.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 (nothing is instrumented)--include "[coverlet.*]Coverlet.Core.Coverage"
=> Includes the Coverage class in theCoverlet.Core
namespace belonging to any assembly that matchescoverlet.*
(e.gcoverlet.core
)--include "[coverlet.*.tests?]*"
=> Includes all types in any assembly starting withcoverlet.
and ending with.test
or.tests
(the?
makes thes
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.
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
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/'
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.
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 theCoverlet.Core
namespace belonging to any assembly that matchescoverlet.*
(e.gcoverlet.core
)/p:Exclude="[*]Coverlet.Core.Instrumentation.*"
=> Excludes all types belonging toCoverlet.Core.Instrumentation
namespace in any assembly/p:Exclude="[coverlet.*.tests?]*"
=> Excludes all types in any assembly starting withcoverlet.
and ending with.test
or.tests
(the?
makes thes
optional)/p:Exclude=\"[coverlet.*]*,[*]Coverlet.Core*\"
=> Excludes assemblies matchingcoverlet.*
and excludes all types belonging to theCoverlet.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 (nothing is instrumented)/p:Include="[coverlet.*]Coverlet.Core.Coverage"
=> Includes the Coverage class in theCoverlet.Core
namespace belonging to any assembly that matchescoverlet.*
(e.gcoverlet.core
)/p:Include="[coverlet.*.tests?]*"
=> Includes all types in any assembly starting withcoverlet.
and ending with.test
or.tests
(the?
makes thes
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 (,
). If you specify multiple filters, then you'll have to escape the surrounding quotes like this: /p:Exclude=\"[coverlet.*]*,[*]Coverlet.Core*\"
or /p:Include=\"[coverlet.*]*,[*]Coverlet.Core*\"
.
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.
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.