Recently I had an issue at work, we wanted to guarantee we had no breaking public API changes, and wanted to start adhering to semantic versioning.

The interesting thing about Semantic versioning is that often people accidentally break the semantic version. So I wrote a unit test which solves this problem

[Fact]
public void phoenix_has_no_public_api_changes()
{
    // arrange
    var phoenix = typeof(IPhoenixHost).Assembly;

    // act
    var publicApi = CodeGen.CreatePublicApiForAssembly(phoenix);

    // assert
    var reporter = new DiffReporter();
    Approvals.Approve(new ApprovalTextWriter(publicApi), new XUnitTestFrameworkNamer(), reporter);
}

What it does

This test is actually quite simple, we grab the assembly, I then have a class which generates the public API for that assembly as a string. I then use Approval Tests to approve any API changes with a diff tool.

So what does that actually look like:

How do I use it?

Add the ApiApprover NuGet package

It will drop a few files into your test project
PublicApiGenerator.cs
PublicApiApprovalTest.cs

Open up PublicApiApprovalTest and fix up the compilation error (specify assembly, and properly attribute up the test for your framework of choice. Then get started!

The source is also available at https://github.com/JakeGinnivan/ApiApprover