Refactoring of simple Model test for Rails (See related posts)

# =============================================================================
# Purpose: Refactored TestCase for simple Rails ActiveRecord::Base and 
#          ActiveForm classes.
# Author:  Manuel Holtgrewe <purestorm at ggnore dot net>
# License: Public Domain
#
# Feel free to flesh out the tests further and make it a more poweful library.
# Drop me a line if you find the module useful or if you created something more
# powerful on top of it.
# =============================================================================
#
# Include this module in your test classes. Then, you define some valid data,
# the model class to test and some "patches" to the valid data to make it invalid.
#
# Sure, this will only work for very simple models but you want to spend as few
# time on those as possible, right?
#
# Assuming you have the following model:
#
#   class MyModel < ActiveRecord::Base
#     validates_length_of :title, :in => 10..100
#     validates_numericality_of :number
#   end
#
# You can then write the following TestCase:
#
#  class MyModelTest < Test::Unit::TestCase
#    include SimpleMethodTests # The basic tests are defined in this module.
#
#    fixtures :my_models
#
#    def setup
#      @model_class = MyModel
#      @valid_data = { :title => 'Abracabra!', :number => 10 }
#      @invalid_patches =
#        [
#          [ :title, nil ], [ :title, 'a' * 9 ], [ :title, 'a' * 101 ],
#          [ :number, nil ], [ :number, 'a' ], [ :title, '123a' ],
#        ]
#    end
#
#    def test_a_nonbasic_test
#      flunk, "Wheee!"
#    end
#
#    # Overwrite a test from the mixin.
#    def test_valid_should_return_false_and_add_errors_with_invalid_data
#      assert true, "Removing this test!"
#    end
#  end
#
# You can both test ActiveRecord::Base and ActiveForm classes (CRUD is not tested
# on ActiveForm classes). If you test ActiveRecord::Base classes then you have to
# provide at least one fixture.
module SimpleModelTests
  def test_valid_should_return_true_with_valid_data
    # Do not use Model.new(attributes) since some might be marked as protected.
    model = @model_class.new
    @valid_data.each { |key, value| model.send("#{key}=".to_sym, value) }

    assert model.valid?
    assert_equal 0, model.errors.count
  end
  
  def test_valid_should_return_false_and_add_errors_with_invalid_data
    @invalid_patches.each do |key, value|
      invalid_data = @valid_data.dup
      invalid_data[key] = value
    
      # Do not use Model.new(attributes) since some might be marked as protected.
      model = @model_class.new
      invalid_data.each { |invalid_key, invalid_value| model.send("#{invalid_key}=".to_sym, invalid_value) }

      assert !model.valid?, "invalid_data[#{key.inspect}] == #{value.inspect}, errors: #{model.errors.full_messages.join('; ')}"
      
      # If the property we set was a foreign key named NAME_id then the error 
      # gets added to the property NAME of the object if the object is an
      # ActiveRecord::Base object.
      if key.to_s =~ /^(.*)_id$/ and model.respond_to?($1.to_sym) then
        assert_not_nil model.errors.on($1.to_sym), "invalid_data[#{$1.to_sym.inspect}] == #{value.inspect}"
      else
        assert_not_nil model.errors.on(key), "invalid_data[#{key.inspect}] == #{value.inspect}"
      end
    end
  end
  
  def test_create_should_work_correctly
    # We only want to test this if we test an ActiveRecord::Base class.
    return if not @model_class.new.respond_to?(:save)
    
    old_count = @model_class.count
    
    # Do not use Model.new(attributes) since some might be marked as protected.
    model = @model_class.new
    @valid_data.each { |key, value| model.send("#{key}=".to_sym, value) }
    
    assert model.save, "errors: #{model.errors.full_messages.join('; ')}"
    assert model.reload
    
    assert_equal old_count+1, @model_class.count
  end
  
  def test_update_should_work_correctly
    # We only want to test update if the model objects have a method "save".
    return if not @model_class.new.respond_to?(:update)
    
    # We assume that there is at least one valid record in the database with
    # different data than the @valid_data you specified above.
    #
    # We order by id to make the result predictable.
    model = @model_class.find(:first, :order => 'id ASC')
    
    @valid_data.each { |key, value| model.send("#{key}=".to_sym, value) }
  
    assert model.save, "errors: #{model.errors.full_messages.join('; ')}"
    assert model.reload
    
    @valid_data.each do |key, value|
      case value
      when Float then
        assert_in_delta value, model.send(key), 0.01
      else
        assert_equal value, model.send(key)
      end
    end
  end
  
  def test_destroy_should_work_correctly
    # We only want to test this if we test an ActiveRecord::Base class.
    return if not @model_class.new.respond_to?(:destroy)
    
    old_count = @model_class.count
    
    model = @model_class.find(:first)
    
    id = model.id
    
    model.destroy
    
    assert_raises(ActiveRecord::RecordNotFound) { @model_class.find(id) }
    
    assert_equal old_count-1, @model_class.count
  end
end