NUnit 3：是否会抛出确切类型的异常？

Question

How can I assert that no exception of the exact type was thrown in my code?

Both

Assert.That(testDelegate, Throws.Nothing); // any type of an exception was not thrown

and

Assert.That(testDelegate, Throws.InstanceOf<ExactException>()); // an exception of needed type was thrown

are not correct way here

Answer 1

It sounds like you want

Assert.That(testDelegate, Throws.TypeOf<ExactException>());

InstanceOf means "of the exact type or a derived type" - just like how is works. We use TypeOf to mean it must be the exact type. It creates an ExactTypeConstraint .

OTOH, if you want to make a negative test (that it does not throw ExactException ) then you can't use the fluent syntax. You could specify the constraint expression directly, like this...

Assert.That(testDelegate, 
    new NotConstraint(
        new ThrowsConstraint(
            new ExactTypeConstraint(typeof(ExactException)))));

I'm not recommending that, but it's available. I'd use Rob's workaround if I had to do this, but I'd also question why I was doing it and hopefully find a way to avoid a situation where any exception except a certain one is OK.

Answer 2

NUnit does not have a constraint that says something like Does.Not.Throw.TypeOf<ExactException>() and passes for/ignores other exceptions. It is a fairly rare use case to test that a method does not throw a specific exception, but pass if any other exception is thrown. To me, it is a code smell , but if you really want to do it, you can get the behavior you want like this,

[Test]
public void DoesNotThrowSpecificException()
{
    try
    {
        MethodThatShouldntThrowExactException(); // But may throw any other exception
    }
    catch (Exception ex)
    {
        Assert.That(ex, Is.Not.TypeOf(typeof(ExactException)));
    }
}