How to fake throwing an exception? - fakeiteasy

Question

I have following setup
A.CallTo(() => fakeChargeService
.CreateAsync(A<ChargeCreateOptions>._, A<RequestOptions>._, A<CancellationToken>._))
.Throws<StripeException>((se) => stripeException);
and then I assert
var msg = await Assert.ThrowsAsync<StripeException>(async () => await mediator.Send(command, CancellationToken.None));
which eventually executes this piece of code
var policyResult = await Policy.Handle<StripeException>(x => x.ShouldRetry())
.WaitAndRetryAsync(new[]
{
TimeSpan.FromSeconds(0.5),
TimeSpan.FromSeconds(1),
TimeSpan.FromSeconds(2),
})
.ExecuteAndCaptureAsync(async () => await this.chargeService.CreateAsync(options, null, cancellationToken));
and here I get error
Assert.Throws() Failure
Expected: typeof(Stripe.StripeException)
Actual: typeof(FakeItEasy.Configuration.FakeConfigurationException): The faked method has the signature (Stripe.ChargeCreateOptions, Stripe.RequestOptions, System.Threading.CancellationToken), but throws was used with (Stripe.StripeException).
I am not sure what is it that I am doing wrong. Any help would be appreciated

Answer 1

You seem to be specifying the wrong signature in your Throws. CreateAsync takes (Stripe.ChargeCreateOptions, Stripe.RequestOptions, System.Threading.CancellationToken), but Throws was used with (Stripe.StripeException).
See the second example in Throwing Exceptions:
// Pass up to 4 original call argument values into the method that creates the exception.
A.CallTo(() => fakeShop.NumberOfSweetsSoldOn(A<DateTime>._))
.Throws((DateTime when)=>new InvalidDateException(when + " is in the future"));
Note that the signature of the lambda and the called method match.
You should update your lambda to match the proper signature. Or better yet, just replace with
.Throws<StripeException>(stripeException)
since there doesn't appear to be any reason to lazily throw, based on the snippet of code you provided.