chefspec: Stub library problem

Let me write a note here

CAUSE

When ChefSpec::SoloRunner.converge is called, Chef::Client#setup_run_context will be called at

From: /opt/chef/embedded/lib/ruby/gems/2.1.0/gems/chefspec-4.2.0/lib/chefspec/solo_runner.rb @ line 106 ChefSpec::SoloRunner#converge:

    105: def converge(*recipe_names)
    106:   node.run_list.reset!
    107:   recipe_names.each { |recipe_name| node.run_list.add(recipe_name) }
    108:
    109:   return self if dry_run?
    110:
    111:   # Expand the run_list
    112:   expand_run_list!
    113:
    114:   # Setup the run_context
 => 115:   @run_context = client.setup_run_context
    116:
    117:   # Allow stubbing/mocking after the cookbook has been compiled but before the converge
    118:   yield if block_given?
    119:
    120:   @converging = true    121:   @client.converge(@run_context)
    122:   self
    123: end

and, blah blah, it will finally Kernel.load libraries at Chef::RunContext::CookbookCompiler#load_libraries_from_cookbook

# lib/chef/run_context/cookbook_compiler.rb
187       def load_libraries_from_cookbook(cookbook_name)
188         files_in_cookbook_by_segment(cookbook_name, :libraries).each do |filename|
189           begin
190             Chef::Log.debug("Loading cookbook #{cookbook_name}'s library file: #{filename}")
191             Kernel.load(filename)
192             @events.library_file_loaded(filename)
193           rescue Exception => e
194             @events.library_file_load_failed(filename, e)
195             raise
196           end
197         end
198       end

Notice that it is load, not require.

So, when you write libraries and spec:

# libraries/helper.rb
module MyHelper
  def self.function; end
end

require_relative "../../libraries/helper"

describe "cookbook::recipe" do
  before do
    allow(MyHelper).to receive(:function)
    # Here, you are stubbing MyHelper.function, but!!!
  end

  let(:chef_run) { ChefSpec::SoloRunner.converge(described_recipe) }
  # In side convergence, libraries are loaded again, and the stubbing is overwritten by real implemntation!

  it "does something" do
    expect(chef_run).to be
  end
end

Here, you are stubbing MyHelper.function, but

  before do
    allow(MyHelper).to receive(:function)
  end

Inside converge, libraries are loaded again, and the stubbing is overwritten by real implemntation

  let(:chef_run) { ChefSpec::SoloRunner.converge(described_recipe) }

HOW TO RESOLVE

Write libraries as following not to be loaded again:

# libraries/helper.rb
module MyHelper
  def self.function; end
end unless defined?(MyHelper)