Contrast

This gem is meant to assist in comparing objects to others, most notably in tests and specs.

Usage

Require contrast.

require 'contrast'

Let's say you have two objects, like so:

john = Person.new first_name: 'John', last_name: 'Galt', gender: 'm'
howard = Person.new first_name: 'Howard', last_name: 'Roark', gender: 'm'

You can contrast the two objects, providing the attributes by which to compare them:

john.contrast_with howard, [:first_name, :last_name, :gender]
# {:first_name=>{:actual_value=>"Howard", :expected_value=>"John"},
#  :last_name=>{:actual_value=>"Roark", :expected_value=>"Galt"}}

Note that it did not show a result for gender, as they matched.

If you call contrast_with!, an exception will be thrown if the two objects do not match based on the provided fields.

john.contrast_with! howard, [:first_name, :last_name, :gender]
# An exception was just thrown, showing the fields that do not match in the message.

You can also compare objects to hashes, and hashes to hashes:

john.contrast_with { first_name: 'Dagny', gender: 'f' }, [:gender]
# {:gender=>{:actual_value=>"m", :expected_value=>"f"}}

If you pass a hash to contrast_with, it will use the keys in the hash if a list of fields is not supplied.

john.contrast_with { first_name: 'Dagny', gender: 'f' }
# {:gender=>{:actual_value=>"m", :expected_value=>"f"}}