Assert.ThrowsAsync
The Assert.ThrowsAsync is the async equivalent to Assert.Throws for asynchronous code. See Assert.Throws for more information.
Exception Assert.ThrowsAsync(Type expectedExceptionType, AsyncTestDelegate code);
Exception Assert.ThrowsAsync(Type expectedExceptionType, AsyncTestDelegate code,
string message, params object[] params);
Exception Assert.ThrowsAsync(IResolveConstraint constraint, AsyncTestDelegate code);
Exception Assert.ThrowsAsync(IResolveConstraint constraint, AsyncTestDelegate code,
string message, params object[] params);
TActual Assert.ThrowsAsync<TActual>(AsyncTestDelegate code);
TActual Assert.ThrowsAsync<TActual>(AsyncTestDelegate code,
string message, params object[] params);
In the above code AsyncTestDelegate is a delegate of the form Task AsyncTestDelegate(), which is used to execute the code in question. This will likely be a lambda expression.
The following example shows the most common way of writing tests.
[TestFixture]
public class AssertThrowsTests
{
[Test]
public void Tests()
{
// Using a method as a delegate
Assert.ThrowsAsync<ArgumentException>(async () => await MethodThatThrows());
}
async Task MethodThatThrows()
{
await Task.Delay(100);
throw new ArgumentException();
}
}
This example shows use of the return value to perform additional verification of the exception. Note that you do not need to await the result.
[TestFixture]
public class UsingReturnValue
{
[Test]
public async Task TestException()
{
MyException ex = Assert.ThrowsAsync<MyException>(async () => await MethodThatThrows());
Assert.That(ex.Message, Is.EqualTo("message"));
Assert.That(ex.MyParam, Is.EqualTo(42));
}
}