Name your MiniTest::Mock for more descriptive errors.

gistfile1.txt

MiniTest::Mock errors are especially vague, particularly when you need more than one mock in your test.
To improve things slightly, add this to the bottom of your test_helper...

module MiniTest
  class NamedMock < Mock
    attr_reader :name

    def initialize(name)
      @name = name
      super()
    end 

    def method_missing(sym, *args, &block)
      super(sym, *args, &block)
    rescue NoMethodError, MockExpectationError, ArgumentError => error
      raise(error.class, "#{error.message} (mock:#{name})")
    end 
  end 
end

Then use NamedMock instead of Mock...

let(:mock_foobar) { MiniTest::NamedMock.new('foobar') }
let(:mock_shazam) { MiniTest::NamedMock.new('shazam') }

And, Voilà...

NoMethodError: unmocked method :frozen?, expected one of [] (mock:shazam)