Open Source Code Coverage Tool for .NET

In computer science, code coverage is a measure used to describe the degree to which the source code of a program is tested by a particular test suite. A program with high code coverage has been more thoroughly tested and has a lower chance of containing software bugs than a program with low code coverage.

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OpenCover – an open source code coverage tool for .NET

An open source code coverage tool (branch and sequence point) for all .NET Frameworks 2 and above (including Silverlight). Also capable of handling 32 and 64 bit processes. Use ReportGenerator for best viewing results (also available via Nuget).

To install OpenCover – an open source code coverage tool for .NET, run the following command in the Package Manager Console

PM> Install-Package OpenCover

OpenCover does not directly execute your tests but instead needs to execute another application that executes your tests in this case we are using MSTest.

First lets create a batch file that we can execute our tests from the command line:

OpenCover.Console -register:Administrator -target:”C:\Program Files (x86)\Microsoft Visual Studio 10.0\Common7\IDE\MSTEST.exe” -targetdir:”D:\Source\Build\Test” -targetargs:”/testcontainer:MySoftware.Test.dll” -filter:”+[*]* -nodefaultfilters -mergebyhash -output:results.xml -target :< target application>

It can be a directory of executable file Nunit or MSTEST.


It is the application directory whose code coverage needs to be executed. It should contain all referenced dlls along with PDB files (which is mandatory for code coverage).


Parameters supported for the target application.

-filter :< space separated filters>

A list of filters to apply to selectively include or exclude assemblies and classes from coverage results. Filters have their own format ± [module-filter]class-filter. If no filter(s) are supplied then a default includes all filter is applied +[*]*. As can be seen you can use an * as a wildcard. Also an exclusion filter (-) takes precedence over an inclusion filter (+).


A list of default exclusion filters are usually applied, this option can be used to turn them off. The default filters are:

Under some scenarios e.g. using MSTest, an assembly may be loaded many times from different locations. This option is used to merge the coverage results for an assembly regardless of where it was loaded assuming the assembly has the same file-hash in each location.

-output :< results file name>

Coverage results will get stored in the above file and it resides in the opencover directory or the specified location in the parameter. When executed, OpenCover will produce an XML file (default results.xml) that contains all the data related to that test run.


ReportGenerator converts XML reports generated by PartCover, OpenCover or NCover into a readable report in various formats. The reports do not only show the coverage quota, but also include the source code and visualize which line has been covered.

ReportGenerator supports merging several reports into one. It is also possible to pass one XML file containing several reports to ReportGenerator (e.g. a build log file).

The following output formats are supported by ReportGenerator:

  • HTML, HTMLSummary
  • XML, XMLSummary
  • Latex, LatexSummary
  • TextSummary
  • Custom reports

D:\downloads\ReportGenerator_1.6.1.0\bin>ReportGenerator “D:\Source\Build\Test\results.xml” “D:\downloads\opencover.4.0.804\”

If we open the produced coverage output (coverage\index.htm) we can see the visualization of the coverage of our target code.

Reference Link:

Hope this will help !!!

Jay Ganesh



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