movement_test.rb

require 'test_helper'

module PongGame
  class MovementTest < TestCase::Functional
    focuses_on Player

    # Test that the left player is initially rendered 120px from the left edge
    # of the window and that the right player is rendered 120px from the right
    # edge.
    def test_stationary
      window.cycle do
        assert_rectangle do |r|
          r.position_x = DISTANCE_FROM_EDGE
          r.position_y = INITIAL_POSITION_Y
          r.width      = WIDTH
          r.height     = HEIGHT
          r.color      = COLOR
        end

        assert_rectangle do |r|
          r.position_x = Window::WIDTH - DISTANCE_FROM_EDGE - WIDTH
          r.position_y = INITIAL_POSITION_Y
          r.width      = WIDTH
          r.height     = HEIGHT
          r.color      = COLOR
        end
      end
    end

    # Test that both players will accelerate linearly from minimum to maximum
    # velocity when their respective up/down buttons are held down.
    def test_acceleration
      [
        [true,  :-],
        [false, :+]
      ].each do |up, operator|
        window.players.each do |player|
          values_for_direction = ->(up) { up ? [false, true] : [false] }

          window.stubs(:button_down?).with(player.up_button).returns(*values_for_direction.(up))
          window.stubs(:button_down?).with(player.down_button).returns(*values_for_direction.(!up))
        end

        assert_velocity_change(0..MAXIMUM_VELOCITY, operator)

        reset_window
      end
    end

    # Test that both players will decelerate linearly from maximum to minimum
    # velocity when you let go of their respective up/down buttons.
    def test_deceleration
      [
        [true,  :-],
        [false, :+]
      ].each do |up, operator|
        window.players.each do |player|
          window.stubs(:button_down?).with(player.up_button).returns(up)
          window.stubs(:button_down?).with(player.down_button).returns(!up)
        end

        window.cycle(times: MAXIMUM_VELOCITY)

        window.players.each do |player|
          window.stubs(:button_down?).with(player.up_button).returns(false)
          window.stubs(:button_down?).with(player.down_button).returns(false)
        end

        assert_velocity_change(MAXIMUM_VELOCITY..0, operator)
      end
    end

    private

    # Assert a linear acceleration/deceleration. Example:
    #
    #     assert_velocity_change(1..15, PongGame::Window.new, ->(initial, offset) { initial - offset })
    #
    # Asserts an acceleration from 1 to 15. The lambda is used to calculate the
    # vertical position. Here we assume an upwards acceleration on the screen,
    # hence the subtraction.
    def assert_velocity_change(range, operator)
      range.inject do |offset, acceleration_or_deceleration|
        position_y = INITIAL_POSITION_Y.send(operator, offset)

        window.cycle do
          window.players.each do |player|
            assert_rectangle do |r|
              r.position_x = player.position_x
              r.position_y = position_y
              r.width      = WIDTH
              r.height     = HEIGHT
              r.color      = COLOR
            end
          end
        end

        if range.begin < range.end
          offset += acceleration_or_deceleration
        else
          offset -= acceleration_or_deceleration
        end
      end
    end
  end
end