Normally, I mock my repo like so:
var repository = new Mock<ISRepository>();
repository.Setup(r => r.GetMemberAsync(email))
.Returns(Task.FromResult(new Member
{
FirstName = firstName,
LastName = lastName
}));
But, in my code, I check to see if the member is not found, i.e. GetMemberAsync returns null. How do I mock this?
I tried:
var repository = new Mock<ISRepository>();
repository.Setup(r => r.GetMemberAsync(email))
.Returns(Task.FromResult<object>(null));
but I get a compile error.
Task represents the execution of the asynchronous method, so for an asynchronous method to return a null task is like telling the calling code "you didn't really just call this method" when of course it did. So, a Task / Task<T> returned from a method should never, ever be null .
Unlike async void unit tests that are quite complicated, you can have async Task unit tests, i.e., unit tests that return a Task instance. Almost all the unit test frameworks (MSTest, NUnit, etc.) provide support for such unit tests.
You get a compiler error because you return a task that doesn't match the type the async method returns. You should return Task<Member>
instead of simply Task<object>
:
repository.Setup(r => r.GetMemberAsync(email)).Returns(Task.FromResult<Member>(null));
It is also possible to return the result without using the Task class.
repository
.Setup(r => r.GetMemberAsync(email))
.ReturnsAsync((Member)null);
Old question but you can also do this which I think it cleaner:
Assuming the default value of your object is null you can also use:
default(<insert object type here>)
e.g.
default(Member)
default(List<string>)
etc.
Full Example:
var myRepo = new Mock<IMyRepo>();
myRepo
.Setup(p => p.GetAsync("name"))
.ReturnsAsync(default(List<string>));
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