method_double_spec.rb

require "bundler/inline"

gemfile do
  source "https://rubygems.org"
  gem "rspec"
end

require "rspec/autorun"

RSpec.describe "method double test" do
  class App
    def foo(*args, **kwargs)
      bar(*args, **kwargs)
    end
  
    def bar(*args, **kwargs)
      p args, kwargs
    end
  end
  
  it "with kwargs" do
    app = App.new
    expect(app).to receive(:bar).with("arg", a: :b)
    app.foo("arg", a: :b)
  end

  it "without kwargs" do
    app = App.new
    # expect(app).to receive(:bar).with("arg")
    expect(app).to receive(:bar).with("arg", **{})
    app.foo("arg")
  end
end