Unit testing (Rails) ActiveRecord classes without a database

On Christmas Jay blogged about unit testing ActiveRecord classes:

class PhoneNumberTest < Test::Unit::TestCase
  Column = ActiveRecord::ConnectionAdapters::Column

  test "to_formatted_s returns US format" do
    PhoneNumber.stubs(:columns).returns([Column.new("digits", nil, "string", false)])
    number = PhoneNumber.new(:digits => "1234567890")
    assert_equal "(123) 456-7890", number.to_formatted_s
  end
end

We don't hit the database in unit tests. Having disabled database access on our unit tests, I started using the above approach to write some unit tests for some active record classes that did not have suitable unit tests. On writing a couple of tests though, it was clear this would be too cumbersome:

class PersonTest < Test::Unit::TestCase
  Column = ActiveRecord::ConnectionAdapters::Column

  test "full name concatenates" do
    Person.stubs(:columns)
          .returns(
          [Column.new("first_name", nil, "string", false), 
           Column.new("middle_initial", nil, "string", false), 
           Column.new("last_name", nil, "string", false)])
    person = Person.new(:first_name => "Ross", 
                        :middle_initial=>"J", 
                        :last_name=>"Pettit")
    assert_equal "Ross J Pettit", person.full_name
  end
end

Jay suggested a fluent interface:

class PersonTest < Test::Unit::TestCase
  test "full name concatenates" do
    person = disconnected(Person).where(:first_name => "Ross", 
                                        :middle_initial=>"J", 
                                        :last_name=>"Pettit")
    assert_equal "Ross J Pettit", person.full_name
  end
end

Finally, here's how we implemented it:

class Test::Unit::TestCase
 class ActiveRecordUnitTestHelper
   attr_accessor :klass

   def initialize klass
     self.klass = klass
     self
   end

   def where attributes
     klass.stubs(:columns).returns(columns(attributes))
     instance = klass.new(attributes)
     instance.id = attributes[:id] if attributes[:id] #the id attributes works differently on active record classes
     instance
   end
      
      protected
   def columns attributes
     attributes.keys.collect{|attribute| column attribute.to_s, attributes[attribute]}
   end

   def column column_name, value
     ActiveRecord::ConnectionAdapters::Column.new(
  column_name, nil,
  ActiveRecordUnitTestHelper.active_record_type(value.class), 
  false)
   end
  
   def self.active_record_type klass
     return case klass.name
       when "Fixnum"         then "integer"
       when "Float"          then "float"
       when "Time"           then "time"
       when "Date"           then "date"
       when "String"         then "string"
       when "Object"         then "boolean"
     end
   end
 end

 def disconnected klass
   ActiveRecordUnitTestHelper.new(klass)
   end
end