test_throws message confuses me

[matrixmorpheus]

There’s nothing I can say that will explain it for you. See for yourself.

julia> @test_throws DomainError throw(DomainError)
ERROR: test failed: DomainError was thrown instead of DomainError
in expression: throw(DomainError)
in error at error.jl:21
in default_handler at test.jl:27
in do_test_throws at test.jl:69

[ihnorton]

The issue is that run_test_throws checks isa not is -- it only checks whether the thrown error is an instance of the given type, but not the type itself. This works:

@test_throws DomainError throw(DomainError())

It's an easy change, but I'm not really sure if there might be some other implication.

[ivarne]

That message is really confusing. It should be pretty simple to check is when isa is false and instruct the caller to throw an instance instead of a type.

@StefanKarpinski is it considered valid to throw a type?

[JeffBezanson]

Julia makes it too easy to define

error{E<:Exception}(::Type{E}) = throw(E())

and so in some places the idiom error(DomainError) is used. I've never liked this however.

[ivarne]

See also #9690