RSpec is ignoring my rescue block in controller - ruby-on-rails

Question

I have a Rails controller which does a health check of the database, like this:
def health_check
begin
status = ActiveRecord::Base.connected? ? 'UP' : 'DOWN'
rescue
status = 'DOWN'
end
render text: status
end
I'm trying to create a RSpec controller spec for this, and the specs for positive and negative responses work, but when I try to test the rescue block, RSpec seems to be ignoring it:
RSpec.describe(HealthCheckController) do
context 'When the check raises an exception' do
before :each do
allow(ActiveRecord::Base).to receive(:connected?).and_raise(OCIException) # Using Oracle
end
it 'should render text DOWN' do
# First attempt
get :health_check
expect(response.body).to eq 'DOWN'
# Second attempt
expect { get :health_check }.to raise_error
expect(response.body).to eq 'DOWN'
end
end
end
I tried the spec with both of the code inside the it block above (separatedly).
For the first, RSpec failed with this:
Failure/Error: get :health_check
OCIException:
OCIException
For the second, it also failed, with this more "familiar" message instead:
Failure/Error: expect(response.body).to eq 'DOWN'
expected: "DOWN"
got: ""
(compared using ==)
I also checked the HTTP code being returned by response, and it's 200, so the response itself is fine, no 500 error.
It's as if RSpec is simply bypassing the rescue block and not running it. What may be causing this? I'm not using the bypass_rescue RSpec method anywhere, this is also a new project.
Using:
Rails 4.2.6
Rake 10.5.0
RSpec-core 3.3.2
RSpec-rails 3.3.3

Answer 1

Actually, the problem has nothing to do with the rescue block in your controller. Rather, it is caused by the fact that you have overriden ActiveRecord::Base#connected? by stubbing it in your before block.
Calling render in the controller initiates a connection to the database. Somewhere in the process ActiveRecord::Base#connected? gets called (twice, actually), but instead of returning what it is supposed to return, it raises an exception that you have defined in your setup.
In your first example, the exception is raised before your expectation, thus the explicit exception name in the failure message.
In your second example, the exception is suppressed by your raise_error expectation, so RSpec is able to proceed to the next one. Where it fails because the render call in the controller never runs (due to the error), and as a result, the response body never gets a chance to be populated.
As a confirmation that ActiveRecord::Base#connected? does get called when you call render, try running the following spec. You will see that it's green, meaning that the said method has been called twice in the process. You can also try replacing render with head :ok and will see that in this case ActiveRecord::Base#connected? gets called only once.
RSpec.describe ApplicationController do
controller do
def index
render json: ''
end
end
specify 'test' do
expect(ActiveRecord::Base).to receive(:connected?).twice
get :index
end
end