ApiApprover

Feb 19 2012

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 accidently 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:
ApiChange

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

Posted by: Jake Ginnivan
Last revised: 20 Feb, 2012 03:54 AM

Comments

Llewellyn Falco

19 Feb, 2012 09:38 PM

Love it! Maintaining a public facing API is so important, yet hardly any attention is paid to ensuring it is consistent.

I should mention that if you grab the latest version of approval tests from the site, you can simplify the above code to:

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

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

// assert
Approvals.Verify(publicApi);

}

Llewellyn Falco

19 Feb, 2012 09:40 PM

Here's that code again, properly formatted :-)

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

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

   // assert 
   Approvals.Verify(publicApi);
}