Imposter

Project Imposter provides simple test doubles over the wire. It is easy to setup and configure. Project imposter supports stubbing as well as mocking of REST resources.

Imposter package can be referenced from Nuget. Configure Nuget as your package source and install the package.

Install-Package Appify.FluentImposter.AspnetCore

Currently, the package supports AspnetCore projects only.

As a first step, Create a .Net Core console application and build the WebHost.

static void Main(string[] args)
{
    var host =  WebHost.CreateDefaultBuilder(args)
           .UseUrls("http://localhost:5000")
           .UseKestrel()
           .UseStartup<Startup>()
           .Build();

    host.Start();

    Console.ReadLine();
}

This will create a base Url for the imposters.

• Create your first Imposter

Creating an Imposter is easy. Just create a class and implement IImposter interface.

For example, below imposter would stub the REST resource which creates a user.

public class CustomerImposter: IImposter
{
        public Imposter Build()
        {
            return new ImposterDefinition("CustomersStub")
                    .DeclareResource("/api/Customers", HttpMethod.Post)
                    .When(r => r.Content.Contains("Name:Jack"))
                    .Then(new FailedToCreateCustomerResponseCreator())
                    .Build();
        }
}

The Fluent Api helps to build an imposter easily. In this case, an imposter with name CustomersStub is being built, which stubs a REST resource http://localhost:5000/api/Customers and accepts Post requests.

You can define conditions when this imposter should be invoked. In this case, when the request body contains an email address [email protected] then this imposter will be invoked and will respond with a fake response.

• Creating fake response.

Fake responses are easy to create. Just Create a class and implement IResponseCreator interface as shown below.

public class FailedToCreateCustomerResponseCreator : IResponseCreator
{
        public Response CreateResponse()
        {
            var orderCreatedResponse = new CreateCustomerResponse()
                                       {
                                           Message = "Customer creation failed.",
                                       };

            return new ResponseBuilder().WithContent(orderCreatedResponse, new JsonContentSerializer())
                                        .WithStatusCode(HttpStatusCode.InternalServerError)
                                        .Build();
        }
}

The ResponseBuilder will help you build the Response.

• Use the Imposter

public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }

            ImpostersAsStubConfiguration stubConfiguration =
                    new ImpostersAsStubConfiguration(new StubImpostersBuilder()
                                                             .CreateStubImposters());

            app.UseStubImposters(stubConfiguration);

            /*Uncomment below code when DynamoDB is available at http://localhost:8000*/

            //ImpostersAsMockConfiguration mockConfiguration =
            //        new ImpostersAsMockConfiguration(new MockImpostersBuilder()
            //                                                 .CreateMockImposters(),
            //                                         new MocksDataStore()
            //                                                 .Create());

            //app.UseMockImposters(mockConfiguration);
}

As simple as that. ImpostersAsStubConfiguration accepts an array of Imposters and UseStubImposters extension method of IApplicationBuilder accpets the ImpostersAsStubConfiguration to host the imposters as REST resources.

Apart from the above, you need to call AddRouting on the IServiceCollection instance as shown below. The reason, you'd need to do that is because the imposter middleware creates and add Routes for each imposter REST resource. Without adding routing, imposters will not be able to receive requests from the client.

public void ConfigureServices(IServiceCollection services)
{
    services.AddRouting();
}