Demonstration of why checking your stub parameters is important if you value having.

stubs_spec.rb

class Collaborator
  # not implemented yet because TDD!
end

class ThingThatDoesThings
  def initialize name
    @name = name
  end

  def do_thing with
    Collaborator.new.do_a_thing(@name, with)
  end
end

class BrokenThingThatDoesThings < ThingThatDoesThings
  def do_thing with
    Collaborator.new.do_a_thing(with, @name)
  end
end

describe ThingThatDoesThings do
  it "should ask the Collaborator what do do" do
    combined_thing = "name-var"
    name = "name"
    var = "var"
    allow_any_instance_of(Collaborator).to receive(:do_a_thing)
      .with(name, var).and_return(combined_thing)

    thing = ThingThatDoesThings.new name

    expect(thing.do_thing(var)).to eq combined_thing
  end

  it "should be bad at stubbing" do
    combined_thing = "name-var"
    name = "name"
    var = "var"
    allow_any_instance_of(Collaborator).to receive(:do_a_thing)
      .and_return(combined_thing)

    thing = ThingThatDoesThings.new name

    expect(thing.do_thing(var)).to eq combined_thing
  end
end

describe BrokenThingThatDoesThings do
  it "should ask the Collaborator what do do" do
    combined_thing = "name-var"
    name = "name"
    var = "var"
    allow_any_instance_of(Collaborator).to receive(:do_a_thing)
      .with(name, var).and_return(combined_thing)

    thing = BrokenThingThatDoesThings.new name

    expect(thing.do_thing(var)).to eq combined_thing
  end

  it "should be bad at stubbing" do
    combined_thing = "name-var"
    name = "name"
    var = "var"
    allow_any_instance_of(Collaborator).to receive(:do_a_thing)
      .and_return(combined_thing)

    thing = BrokenThingThatDoesThings.new name

    expect(thing.do_thing(var)).to eq combined_thing
  end
end

So obviously the Broken* spec should always fail, however, because we failed to check the parameters of the stub in the bad stubbing scenario, it passes:

ThingThatDoesThings
  should ask the Collaborator what do do
  should be bad at stubbing

BrokenThingThatDoesThings
  should ask the Collaborator what do do (FAILED - 1)
  should be bad at stubbing

And that's why you always check your stub parameters.