From: Brian Candler <b.candler@...>
Date: 2010-08-02T22:53:35+09:00
Subject: Re: Mocking a method with a block

Fernando Guillen wrote:
> Is this possible?.. am I completely lost?.. is there any better way to
> do this?

I'd suggest you use an existing mocking library like "mocha". Example:

-------- 8< ----------------
require 'net/pop'
require 'test/unit'
require 'rubygems'
require 'mocha'

# code to test
class Foo
  attr_reader :opts
  def initialize(opts)
    @opts = opts
  end
  def bar(block)
    Net::POP3.start( opts[:server], opts[:port], opts[:user], 
opts[:pass] ) do |pop|
      pop.each_mail do |m|
        block.call( m )
      end
    end
  end
end

# tests
class MyTest < Test::Unit::TestCase
  def test_1
    mails = ["xxxxx","yyy"]
    mockpop = mock
    mockpop.expects(:each_mail).multiple_yields(*mails)
    Net::POP3.expects(:start).with("127.0.0.1", 110, "a", 
"b").yields(mockpop)

    foo = Foo.new(:server=>"127.0.0.1", :port=>110, :user=>"a", 
:pass=>"b")
    res = []
    foo.bar(lambda { |x| res << x.size })
    assert_equal [5,3], res
  end

  # more expectation-based style
  def test_2
    mails = ["xxxxx","yyy"]
    mockpop = mock
    mockpop.expects(:each_mail).multiple_yields(*mails)
    Net::POP3.expects(:start).with("127.0.0.1", 110, "a", 
"b").yields(mockpop)

    mockblock = mock
    seq = sequence(:block)
    mockblock.expects(:call).with(mails[0]).in_sequence(seq)
    mockblock.expects(:call).with(mails[1]).in_sequence(seq)

    foo = Foo.new(:server=>"127.0.0.1", :port=>110, :user=>"a", 
:pass=>"b")
    foo.bar(mockblock)
  end
end
-------- 8< ----------------

I find there's something unsatisfying about tests which look like this. 
Sometimes you can spend more effort on the mechanics of mocking than on 
solving the original problem, and the resulting tests are closely 
coupled to the internal implementation of your function. But that *is* 
what you asked for :-)

Refactoring might make your code easier to test. e.g.

-------- 8< ----------------
require 'net/pop'
require 'test/unit'
require 'rubygems'
require 'mocha'

class Foo
  attr_reader :opts
  def initialize(opts)
    @opts = opts
  end
  def bar(block)
    for_all_messages do |m|
      block.call(m)
    end
  end
private
  def for_all_messages(&blk)
    Net::POP3.start( opts[:server], opts[:port], opts[:user], 
opts[:pass] ) do |pop|
      pop.each_mail(&blk)
    end
  end
end

class MyTest < Test::Unit::TestCase
  def test_1
    foo = Foo.new({})

    mails = ["xxxxx","yyy"]
    foo.expects(:for_all_messages).multiple_yields(*mails)
    res = []
    foo.bar(lambda { |x| res << x.size })
    assert_equal [5,3], res
  end
end
-------- 8< ----------------

HTH,

Brian.
-- 
Posted via http://www.ruby-forum.com/.