Rspec - Is it possible to stub a hash - ruby

Question

I'm working on some unit tests. One of them use a specific configuration variable as set in my application MyBigApp::Env which looks like:
{:country=>'uk', :another_hosts=>["192.168.99.105"]}
So I access it with MyBigApp::Env.country
However in my unit test I want that country for the test become something.
Using rspec I've seen stub but can't get it to work - any ideas where I'm going wrong:
MyBigApp::Env.stub(:[]).with('country').and_return('gr')
Also tried this (as above shows deprecated):
allow(MyBigApp::Env).to receive('country').and_return('gr')
Infact as a test, I also tried:
my_hash = {:uri=>nil}
allow(my_hash).to receive(:[]).with(:uri).and_return('Over written!')
p my_hash
and that didnt update either - it just returned {:uri=>nil}
As a workaround, at the moment I'm having to save the env var in a temp var in the before(each) block then return it back to the original in the after(each). This feels really risky to me. I'm thinking imagine the service running and someone runs unit tests it could effect the end user in that small instance the test is running.
Any help would be appreciated.
Thanks

Answer 1

Yes it possible, but keep in mind that stub only works when you trigger/call the method that you stubbed/mocked
my_hash = {:uri=>nil}
allow(my_hash).to receive(:[]).with(:uri).and_return('Over written!')
p my_hash[:url] # it will be 'Over written!'

Answer 2

This works for me:
my_hash = {:uri=>nil}
allow(my_hash).to receive(:[]).with(:uri).and_return('Over written!')
expect(my_hash[:uri]).to eq "Over written!"
In your sample test case, you are just calling p my_hash which doesn't actually call the [] method.
In terms of why this isn't working with MyBigApp::Env, well, that really depends on what class it is. Possible whatever method .country is doesn't actually call [].
Really, if you call MyBigApp::Env['country'] and stub MyBigApp::Env to receive [] with 'country', it should work.
In regards to your concern about changing your running application's behavior from the tests ... what kind of tests are these?! Running unit tests against a live production application would be very odd. How do you imagine it would change your production app's code? The Env hash just lives in memory right?
Anyway, you should never have to worry about your tests changing the experience for an 'end user'. Always run tests on a completely quarantined envionment, meaning don't use the same database. Actually, the test database is usually wiped after each test.

Answer 3

Just wanted to suggest a non-stubbing alternative. For example:
def code_under_test
key = 'country'
# ... maybe lots of code
value = MyBigApp::Env[key] # deep inside some classes
# ... lots more code
"This is the #{value}"
end
MyBigApp::Env is hard-coded deep in the code, and the need for stubbing reveals that dependency, and the benefits of OOP encapsulation are lost.
It'd be much easier if this were the case:
def code_under_test(config_vars = MyBigApp::Env)
"This is the #{config_vars['country']}"
end
it 'should return my country value' do
value = previous_code_under_test('country' => 'TEST VALUE')
expect(value).to eq("This is the TEST VALUE")
end
No stubbing required, just plain old method calls.