thoughtbot--shoulda-matchers/lib/shoulda/action_controller/assign_to_matcher.rb

module Shoulda # :nodoc:
  module ActionController # :nodoc:

    # Ensures that the controller assigned to the named instance variable.
    #
    # Options:
    # * <tt>with_kind_of</tt> - The expected class of the instance variable
    #   being checked.
    # * <tt>with</tt> - The value that should be assigned.
    #
    # Example:
    #
    #   it { should assign_to(:user) }
    #   it { should_not assign_to(:user) }
    #   it { should assign_to(:user).with_kind_of(User) }
    #   it { should assign_to(:user).with(@user) }
    def assign_to(variable)
      AssignToMatcher.new(variable)
    end

    class AssignToMatcher # :nodoc:

      def initialize(variable)
        @variable    = variable.to_s
        @check_value = false
      end

      def with_kind_of(expected_class)
        @expected_class = expected_class
        self
      end

      def with(expected_value = nil, &block)
        @check_value       = true
        @expected_value    = expected_value
        @expectation_block = block
        self
      end

      def matches?(controller)
        @controller = controller
        @expected_value = @context.instance_eval(&@expectation_block) if @expectation_block
        assigned_value? && kind_of_expected_class? && equal_to_expected_value?
      end

      attr_reader :failure_message, :negative_failure_message

      def description
        description = "assign @#{@variable}"
        description << " with a kind of #{@expected_class}" if @expected_class
        description
      end

      def in_context(context)
        @context = context
        self
      end

      private

      def assigned_value?
        if !@controller.instance_variables.include?("@#{@variable}")
          @failure_message =
            "Expected action to assign a value for @#{@variable}"
          false
        else
          @negative_failure_message =
            "Didn't expect action to assign a value for @#{@variable}, " <<
            "but it was assigned to #{assigned_value.inspect}"
          true
        end
      end

      def kind_of_expected_class?
        return true unless @expected_class
        if assigned_value.kind_of?(@expected_class)
          @negative_failure_message =
            "Didn't expect action to assign a kind of #{@expected_class} " <<
            "for #{@variable}, but got one anyway"
          true
        else
          @failure_message =
            "Expected action to assign a kind of #{@expected_class} " <<
            "for #{@variable}, but got #{@variable.inspect} " <<
            "(#{@variable.class.name})"
          false
        end
      end

      def equal_to_expected_value?
        return true unless @check_value
        if @expected_value == assigned_value
          @negative_failure_message =
            "Didn't expect action to assign #{@expected_value.inspect} " <<
            "for #{@variable}, but got it anyway"
          true
        else
          @failure_message =
            "Expected action to assign #{@expected_value.inspect} " <<
            "for #{@variable}, but got #{assigned_value.inspect}"
          false
        end
      end

      def assigned_value
        @controller.instance_variable_get("@#{@variable}")
      end

    end

  end
end