Raising an error

Use and_raise to make the test double raise an error when it receives the message. Any of the following forms are supported:

* `and_raise(ExceptionClass)`
* `and_raise("message")`
* `and_raise(ExceptionClass, "message")`
* `and_raise(instance_of_an_exception_class)`

Raising an error

Given a file named “raisesanerror_spec.rb” with:

RSpec.describe "Making it raise an error" do
  it "raises the provided exception" do
    dbl = double
    allow(dbl).to receive(:foo).and_raise("boom")
    dbl.foo
  end
end

When I run rspec raises_an_error_spec.rb

Then it should fail with:

  1) Making it raise an error raises the provided exception
     Failure/Error: dbl.foo

     RuntimeError:
       boom