C# code coverage to near 100%?

What is it?

Code coverage, it is this magical number that will never hit 100% for a larger project, but near 100% should be doable right?

One of my projects is setup using the Clean Architecture and has a separate front end and back end test project.

For this article I will focus on the back end, written in C# with ASP.NET Core 3.1 using Xunit and FluentAssertions.

Most basic test for a helpers class

The challenge

Writing tests like above is straightforward, but a mistake is easaly made.
What mistake you ask?
Well, the one of missing a test implementation of one of the helper methods in my helper class.

As you can see, they have some good naming, but those might look a lot like each other, e.g.:

  • GetCompanyIdFromUser
  • GetIdentityServerIdFromUser
  • GetSubjectIdFromUser

They all start with Get and end with IdFromUser.
In my test class I implement them from top to bottom, like in the example image above in this post

  • GetCompanyIdFromUser_HappyFlow
  • GetCompanyIdFromUser_ThrowsException
  • GetSubjectIdFromUser_HappyFlow
  • GetSubjectIdFromUser_ThrowsException

And there it is, the sneaky mistake, the tests for GetIdentityServerIdFromUser are missing.

Identity the missing tests using tools

Some options to identify are widely available

But all of them at the moment of writing didn’t show me in a simple way that I was missing to test on of my helper methods.

I based my solution on a blog post on medium from Krishna Mohan: https://medium.com/swlh/generating-code-coverage-reports-in-dotnet-core-bb0c8cca66
It uses the following steps:

  1. Run dotnet test with a collector
  2. Change the coverage report to a xml version
  3. Generate a html report
The result shows that I miss tests for GetIdentityServerIdFromUser

Automate this report as far as possible

I created a powershell script that does exactely this.

The powershell script and output

How to use it

1. Goto the test project and install the dependencies:
Install-Package Microsoft.CodeCoverage -Version 16.6.1
Install-Package ReportGenerator -Version 4.5.8
2. Place the GenerateTestCoverage powershell script in the test project directory
3. Run it 😀


Some tweaking needs to be done as I will not test migrations with almost 100k lines of code, but is shows that for my core project, I am only just above a quarter, that needs to be improved!

Generated report by the powershell script

2 thoughts on “C# code coverage to near 100%?

    • It can for sure be added to a Azure DevOps build Pipeline. The results will than be in the aftifect directory.
      Should be doable to add those to the dashboard

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