ministub.rb

class MiniStub
  def initialize *args
    unless args.first.is_a? Hash
      @name = args.shift
    end
    @stubbed = args.first || {}
  end

  def inspect
    "#<MiniStub(#{@name})>"
  end

  def stub! name, value = nil, &block
    if value
      @stubbed[name] = value
    elsif block
      @stubbed[name] = block
    else
      @stubbed[name] = nil
    end
  end

  def respond_to? method
    @stubbed.has_key?(method) || super
  end

  def method_missing method, *args
    if @stubbed.has_key? method
      stub = @stubbed[method]
      if stub.respond_to? :call
        stub.call *args
      else
        stub
      end
    else
      super
    end
  end

  module TestHelper
    def stub *args
      MiniStub.new *args
    end
  end
end

require 'minitest/unit'
require 'minitest/autorun'
require 'minitest/pride'

class MiniStubTest < MiniTest::Unit::TestCase
  def test_works
    a_stub = stub

    assert a_stub
  end

  def test_naming
    a_stub = stub :foo

    assert_match /foo/, a_stub.inspect
  end

  def test_query_methods
    a_stub = stub foo: "bar"

    assert_equal "bar", a_stub.foo
  end

  def test_query_callable
    a_stub = stub foo: -> { "bar" }

    assert_equal "bar", a_stub.foo
  end

  def test_method_with_parameters
    a_stub = stub foo: "bar"

    assert_equal "bar", a_stub.foo("baz")
  end

  def test_method_with_parameters
    a_stub = stub foo: ->(a) { a.upcase }

    assert_equal "BAZ", a_stub.foo("baz")
  end

  def test_respond_to_acts_properly
    a_stub = stub foo: "bar"

    assert a_stub.respond_to? :foo
  end

  def test_can_build_stubs_afterwards
    a_stub = stub

    a_stub.stub!(:foo) { "foo" }

    assert_equal "foo", a_stub.foo
  end

  def test_stub_bang_works_with_values
    a_stub = stub

    a_stub.stub! :foo, "bar"

    assert_equal "bar", a_stub.foo
  end

  def test_stub_bang_no_arguments_is_cool
    a_stub = stub

    a_stub.stub! :foo

    a_stub.foo
    assert true # no real assert, just making sure we don't raise
  end

  include MiniStub::TestHelper
end

Nice :)