Question

This example is contrived, please don’t take it verbatim as my code.

I have the need to assert something like the following:

def mymethod
    Dir.chdir('/tmp') do
        `ls`
    end
end

In the end I want to assert that:

1. Dir.chdir is invoked with the appropriate parameters.
2. ` is invoked with the appropriate parameters

I started off with…

Dir.expects(:chdir).with('/tmp')

but after that I’m not sure how to invoke the block passed to Dir.chdir.

Answer 1

You need to use the mocha yields method. Also, writing an expectation for the backtick method is rather interesting. You need to make an expectation like this:

expects("`")

But on what object? You might think on Kernel or Object, but that doesn’t actually work.

As an example, given this module:

module MyMethod
  def self.mymethod
    Dir.chdir('/tmp') do
      `ls`
    end
  end
end

I could write a test like this:

class MyMethodTest < Test::Unit::TestCase
  def test_my_method
    mock_block = mock
    mock_directory_contents = mock
    MyMethod.expects("`").with('ls').returns(mock_directory_contents)
    Dir.expects(:chdir).yields(mock_block).returns(mock_directory_contents)
    assert_equal mock_directory_contents, MyMethod.mymethod
  end
end

Part of the trick is to figure out which object to expect the backtick method to be invoked on. It depends on the context – whatever self is when that method is invoked. Here it is the module MyMethod, but depending on where you define mymethod it will be different.