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.

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

• Visual Studio Live Unit Testing, only for the Enterprise edition
• dotCover from Jetbrains
• Coveralls
• Coverlet
• altcover

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

Automate this report as far as possible

I created a powershell script that does exactely this.

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 😀

Result

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!