double/instance_double argument type

[bquorning]

I'm seeing double/instance_double/class_double/object_double/spy etc. being called with sometimes a string, sometimes a symbol (perhaps because the rspec-mocks documentation explicitly allows both), and of course sometimes a constant referring to a class or module.

I think mixing string and symbol arguments is a bit of a mess, so I would propose making a new cop that enforces either one or the other – with strings being the default enforced style. Why? Because "MyClass" looks better than :MyClass in those cases where you pass in a module name as a string/symbol.

[pirj]

instance_double accepts a class, and so does class_double/instance_spy. I see no good reasons not to use this. Except to avoid excessive class loading when instance_double and the class is referenced from globally-defined shared examples, and those shared examples are eagerly loaded from spec helper.

[pirj]

I can also add that changing from a class literal to a string/symbol arguably makes the cop unsafe unless verify_doubled_constant_names is turned on. It is off by default in RSpec Mocks 3.11 and the upcoming 4.0, too for the reasons I struggle to remember. Related PR turning on verify_partial_doubles by default.

[corsonknowles]

We have a very simple Rubocop rule that autocorrects from string to Class for instance_double. It does not affect symbol declarations. Is there interest in us open-sourcing this? I'd be happy to push it up.

[pirj]

That will be very kind of you, @corsonknowles ! A pr is welcome.

[corsonknowles]

Happy to help! Here's a draft PR:

• Add RSpec/StringAsInstanceDoubleConstant #1957

We've run this on over 25,000 files and had it in place for a few years.

I'm running into a little hiccup with the rake task for documentation (but the ardocs did successfully generate)