Stub a method on a Thor CLI

Question

I have a Thor class that has a getter method defined like this:

# Playgrounds CLI skeleton class.
# Commands are added from commands folder
class CLI < Thor
 def self.exit_on_failure?
 true
 end
 no_commands do 
 def location
 unless @location
 path = Location.detect Dir.pwd
 throw 'Could not find a playgrounds directory' if path.nil?
 @location = Location.new path, File.join(path, '.templates')
 end 
 @location 
 end
 end
end

I am now trying to write a unit test for this class that checks that the wiring is correct (commands correctly hand off to the location instance).

require_relative '../lib/cli'
require_relative '../lib/location'
describe CLI do
 subject (:cli) { described_class.new }
 let (:location) { instance_double(Location) }
 before :each do
 allow(Location).to receive(:detect).and_return('') 
 allow(cli).to receive(:location).and_return(location)
 end
 describe 'playground new NAME' do
 it 'uses the specified name' do
 cli.invoke(:new_playground, ['example_playground'])
 expect(location).to have_received(:new_playground)
 end
 end
end

But the CLI always calls the actual location method, not the stubbed-out one. I think this is because Thor actually creates a new instance, so it doesn't use cli at all.

Based on this, I have tried to replace allow(cli) with

allow_any_instance_of(CLI).to receive(:location).and_return location

This works, but it also produces this rather ugly warning on my console:

[WARNING] Attempted to create command "location" without usage or description. Call desc if you want this method to be available as command or declare it inside a no_commands{} block. Invoked from "/vagrant/vendor/bundle/ruby/3.4.0/gems/rspec-mocks-3.13.5/lib/rspec/mocks/any_instance/recorder.rb:223:in 'Module#alias_method'".

How can I wrap allow_any_instance_of in a Thor no_commands block so that it suppresses the warning? The obvious - CLI.no_commands { allow_any_instance_of ... } doesn't work.

• engineersmnky: Maybe try using a class double with as_stubbed_constant? Another issue might be (untested) that no_commands appears to define the methods in a NestedContext Object. Source. I did not dig any deeper and unfortunately I am not in a position to test at the moment. Adding an example of the :new_playground command might be a useful addition to the post so that true testing is possible

Answer 1

I was able to solve it by adding this:

before do
 ctx = self
 described_class.class_exec do
 no_commands { ctx.allow_any_instance_of(self).to ctx.receive(:location).and_return ctx.location }
 end
end
after do
 described_class.class_exec do
 no_commands { RSpec::Mocks.teardown }
 end
end

Explanation, for posterity:

The key here is to execute the stubbing within the context of the described_class, which allows me to run a no_commands block. Inside that block, I can then do the actual stubbing. Since class_exec changes self, I need to preserve the old self for access to the required methods.

This is almost enough to suppress the warnings, but not quite: After each test, RSpec automatically restores the old methods, and this causes another warning. Therefore, I added an after block, where I do the same thing to manually restore the mocks.