How can I unit test a sitecore commerce engine plugin?

Question

The documentation is not rich of information IMHO and, about this topic, I haven't found anything, at least in the version 8.2.1 (version I'm using). In commerce 9 docs there is only a little paragraph that explain it's possible to unit test but there isn't a single example, even a simple one.

Sincerely I haven't even tried by myself, nonetheless being programmed as interface makes everything simpler but...

Has anyone unit tested a custom sitecore commerce engine plugin? How?

Answer 1

Most services are, as you say, provided as interfaces so it's mostly down to mocking them for your purposes.

Having said that, some things are harder to mock than they first appear. Here's what I use to mock CommercePipelineExecutionContext:

static class FakeCommercePipelineExecutionContext
{
    public static CommercePipelineExecutionContext CreateContext()
    {
        return new CommercePipelineExecutionContext(CreateOptions(), CreateLogger());
    }

    private static ILogger CreateLogger()
    {
        return new NullLogger();
    }

    private static IPipelineExecutionContextOptions CreateOptions()
    {
        return new CommercePipelineExecutionContextOptions(CreateCommerceContext());
    }

    private static CommerceContext CreateCommerceContext()
    {
        var context = new CommerceContext(new NullLogger(), null);

        context.Environment = new CommerceEnvironment();

        return context;
    }
}

class NullLogger : ILogger
{
    public IDisposable BeginScope<TState>(TState state)
    {
        return new NullDisposable();
    }

    public bool IsEnabled(LogLevel logLevel)
    {
        return true;
    }

    public void Log<TState>(LogLevel logLevel, EventId eventId, TState state, Exception exception, Func<TState, Exception, string> formatter)
    {
    }
}

class NullDisposable : IDisposable
{
    public void Dispose()
    {
    }
}

That's enough to make access to policies, models, and objects work as expected. I have tests using that infrastructure that assert that the pipeline was aborted.

Some pipelines like IFindEntityPipeline and IPersistEntityPipeline can also be tricky to mock, so it might be worth creating helpers for them.