gem - RSpec: How can I stub a method on an object, before instantiation, without having to stub all the rest? -

i writing gem rails, includes generator create model. under circumstances, generator supposed call itself, , uses generate method this. works fine when using it.

i using rspec 3.2 generator_spec try , test functionality, being gem, when gets generate call, complains rails doesn't exist:

/path/to/ruby: no such file or directory -- bin/rails (loaderror) 

so have been trying stub generator#generate method make same thing run_generator in spec, before run_generator calls call generate in middle of them. however, of potential solutions, have run problems.

outright overriding class - can't use spec method.

class generator   def generate(*args)     run_generator args[1..-1]   end end 

this raises undefined method 'run_generator'. not surprising.

using partial double - instantiated late.

allow(generator).to receive(:generate) { |*args| run_generator args[1..-1] } 

this perfect, run_generator calls class method behind scenes, generator in question doesn't exist yet.

using instance double - disallows other methods.

recursible = instance_double(generator) allow(recursible).to receive(:generate) { |*args| run_generator args[1..-1] } test_case_instance.generator_class = recursible 

however, using double requires stub all methods on going used - , rest calling original implementations. seems difficult , unnecessary. there way round it?

taryn east ended giving me vital clue: needed full-blown rails app in test directory.

unfortunately, generator_spec's prepare_destination method blows target directory away, here's ended with:

it 'the test'   system "rails new #{destination_root} -bfq" # no bundling, force overwrite, quiet   file.write "#{destination_root}/gemfile", "gem '#{file.basename dir.pwd}', path: '#{dir.pwd}'", mode: 'a'   system "cd #{destination_root} && bundle install --quiet"    # ... continue test before