How to make internal members visible to other assemblies in .net core?

  • Post published:May 3, 2020

When following a Test Driven Development (TDD) approach and adhering to Object-Oriented Programming (OOP) principles, especially encapsulation, tests need to be written to cover internal classes and methods.

To allow internal members in a project to be accessible to a test assembly, simply add the following code block to the csproj file:

When following best practices, unit test project names should be the same name as the assembly that is been tested and ended with .Tests. This is the reason why the above code uses $(AssemblyName).Tests as the name of the test project.

Instead of using $(AssemblyName).Tests, the name of the test assembly can be used directly, example:

Example usage

As an example, create a solution named InternalsDemo with two projects:

  • InternalsDemo – Class Library (.NET Standard)
  • InternalsDemo.Tests – xUnit Test Project (.NET Core)

Install the following nuget packages in the InternalsDemo.Tests project:

  • AutoFixture
  • Moq
  • FluentAssertions

Reference InternalsDemo in the InternalsDemo.Tests project:


In the InternalsDemo project, create the following classes.

Note that the implementation of the HeroService is internal.

In the InternalsDemo.Tests project, add the following test case:

Now that all the classes are set up, build the solution. The build should fail with the following error:

'HeroService' is inaccessible due to its protection level

To resolve this, open the InternalsDemo csproj and add the following code:


You will now be able to build the solution and run the unit test.


Microsoft have provided an easy way for developers to expose internal members in a project to other assemblies. This is done by adding a simple snippet of code in the csproj file.

The source code used in this article can be found here.

Software versions used in this article

  • Visual studio 2019 v4.8.03752
  • .net standard v2.0.3
  • AutoFixture v4.11.0
  • Moq v4.14.1
  • xunit v2.4.1
  • FluentAssertions v5.10.3
  • ReSharper Ultimate v2020.1.1