Unit test with subsituted data for asyncronous webapi - unit-testing

Question

I'm working on an unit test with NUnit for a WebAPI. The Method to test is async and will normally call async a class implementing dapper to access the database. I wanted to fake the data with NSubstitute. this is the API:
public class ModelController : ApiController
{
public async Task<IHttpActionResult> GetAsync()
{
// fake list for testing purposes
List<MyModel> myModels = new List<MyModel>
{
new MyModel
{
ID = 1,
Name = "Test1",
Created = DateTime.Now,
Creator = "Admin"
},
new MyModel
{
ID = 2,
Name = "Test2",
Created = DateTime.Now,
Creator = "Admin"
}
};
return this.Ok(myModels); // <= here would be a call to a class implementing dapper like: return this.Ok(await DbRepo.GetAsync())
}
}
and this is the test:
[TestFixture]
public class ModelControllerTests : ApiController
{
[Test]
public async Task GetAsync_GetAll_ReturnOkHttpResultWithListOfMyModels()
{
private ModelController target = Substitute.For<ModelController>();
List<MyModel> myModels = new List<MyModel>
{
new MyModel
{
ID = 1,
Name = "Test1",
Created = DateTime.Now,
Creator = "Admin"
},
new MyModel
{
ID = 2,
Name = "Test2",
Created = DateTime.Now,
Creator = "Admin"
}
};
OkNegotiatedContentResult<List<MyModel>> result = new OkNegotiatedContentResult<List<MyModel>>(myModels, new ModelController());
(await this.target.GetAsync() as OkNegotiatedContentResult<List<MyModel>>).Returns(result);
OkNegotiatedContentResult<List<MyModel>> actual = (await this.target.GetAsync() as OkNegotiatedContentResult<List<MyModel>>);
Assert.That(actual.Content.Count, Is.GreaterThanOrEqualTo(1)); // <== NullReferenceException because actual is null
}
}
I get a NullReferenceException becaus "actual" is null. But I don't get why. Any ideas?

Answer 1

I'd re-write your test something like this
[TestFixture]
public void GetAsync_GetAll_ReturnOkHttpResultWithListOfMyModels()
{
List<MyModel> expectedModel = new List<MyModel>
{
new MyModel
{
ID = 1,
Name = "Test1",
Created = DateTime.Now,
Creator = "Admin"
},
new MyModel
{
ID = 2,
Name = "Test2",
Created = DateTime.Now,
Creator = "Admin"
}
};
var sut = new ModelController();
var result = sut.GetAsync();
//check you can cast the result first
Assert.That(result.Result, Is.AssignableTo<OkNegotiatedContentResult<IEnumerable<MyModel>>());
var typedResult = (OkNegotiatedContentResult<IList<MyModel>>)result.Result;
//Assert the actual data.
}
Instantiate your ModelController. This is your system under test. You should be using NSubstitute, Moq, FakeItEasy,... to mock/fake out dependencies of your system under test. At this point, you don't have any. You mention Dapper, so you'd want to mock that dependency once you implement it.
You don't need to mark the test method as async either.
Use a hard cast instead of an "as" will result in an exception if it can't cast it which will fail the test. Plus you've already Asserted that this cast should work in the line above.
Also this is just pseudo code it is not guaranteed to run.