other.rb

require "minitest/autorun"
require "mocha"
require "watchable"

describe Watchable do
  subject do
    Object.new.extend Watchable
  end

  it "has an empty list of watchers by default" do
    assert subject.watchers.empty?
  end

  it "returns an empty array of watchers for any event" do
    assert_equal [], subject.watchers[:foo]
  end

  describe :fire do
    it "calls each watcher with optional args" do
      subject.on :foo, mock { expects(:call).with :bar, :baz }
      subject.fire :foo, :bar, :baz
    end

    it "calls multiple watchers in order" do
      fires = sequence "fires"

      subject.on :foo, mock { expects(:call).in_sequence fires }
      subject.on :foo, mock { expects(:call).in_sequence fires }

      subject.fire :foo
    end

    it "returns the watchable" do
      assert_same subject, subject.fire(:foo)
    end
  end

  describe :off do
    it "can unregister a block" do
      b = lambda {}

      subject.on :foo, &b
      subject.off :foo, &b

      assert subject.watchers[:foo].empty?
    end

...