This post originated from an RSS feed registered with Ruby Buzz by Guy Naor. Original Post: Testing: DRYing the Asserting of Array Similarity Feed Title: Famundo - The Dev Blog Feed URL: http://devblog.famundo.com/xml/rss/feed.xml Feed Description: A blog describing the development and related technologies involved in creating famundo.com - a family management sytem written using Ruby On Rails and postgres Latest Ruby Buzz Posts Latest Ruby Buzz Posts by Guy Naor Latest Posts From Famundo - The Dev Blog

After one too many instances of:

ph = contacts(:john).phones.collect{|p| p.number }
assert_equal 3, ph.size
assert_equal []. ['12345', '56789', '67890'] - ph

I decided it's time to DRY up array similarity checking. Using assertequal on arrays is a so-so solution, given that you don't always know if the order in the array is the same. Returning an array from a hasmany collection has a non-deterministic order by default. So asserting that what we get from a collection is a bit painfull, and require the code above to make absolutely sure we got what we wanted.

To make my life easier and DRYer, I added the following function to the test/test_helper.rb file:

def assert_array_similarity(expected, actual, message=nil)
  full_message = build_message(message, "<?> expected but was\n<?>.\n", expected, actual)
  assert_block(full_message) { (expected.size ==  actual.size) && (expected - actual == []) }
end

And now testing for array similarity is simply:

assert_array_similarity ['12345', '56789', '67890'], contacts(:john).phones.collect{|p| p.number }

Not bad, 1 line instead of 3 and better error reporting to boot.