CODEWITHSUNDEEP
c#.netasynchronoustasknsubstitute
Brandon
Brandon

Reputation: 1664

NSubstitute - mock throwing an exception in method returning Task

Using NSubstitute, how do you mock an exception being thrown in a method returning a Task?

Let's say our method signature looks something like this:

Task<List<object>> GetAllAsync();

Here's how NSubstitute docs say to mock throwing exceptions for non-void return types. But this doesn't compile :(

myService.GetAllAsync().Returns(x => { throw new Exception(); });

So how do you accomplish this?

Upvotes: 38

Views: 36719

Answers (5)

John
John

Reputation: 11

This simple line worked for me:

Assert.ThrowsAsync<Exception>(async () => await _service.MyAsyncFunction());

Upvotes: 1

SIbghat
SIbghat

Reputation: 309

in my case it worked as follows

_substiture.GetAsync<SomeType?>("").ThrowsAsyncForAnyArgs(new CustomException(System.Net.HttpStatusCode.InternalServerError, "some message"));

Upvotes: 1

dstj
dstj

Reputation: 5230

Actually, the accepted answer mocks a synchronous exception being thrown, that is not the real async behavior. The correct way to mock is:

var myService = Substitute.For<IMyService>();
myService.GetAllAsync()
         .Returns(Task.FromException<List<object>>(new Exception("some error")));

Let's say you had this code and GetAllAsync()

try
{
    var result = myService.GetAllAsync().Result;
    return result;
}
catch (AggregateException ex)
{
    // whatever, do something here
}

The catch would only be executed with Returns(Task.FromException>(), not with the accepted answer since it synchronously throws the exception.

Upvotes: 47

Maksymilian Mulawa
Maksymilian Mulawa

Reputation: 277

This is what worked for me:

myService.GetAllAsync().Returns(Task.Run(() => ThrowException()));

private List<object> ThrowException()
{
        throw new Exception();
}

Upvotes: 5

Brandon
Brandon

Reputation: 1664

This worked:

using NSubstitute.ExceptionExtensions;

myService.GetAllAsync().Throws(new Exception());

Upvotes: 31

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