add take element screenshot for oss (#33)

* add take element screenshot for oss

* add a unit test

* fix rubocop

Author: KazuCocoa

lib/appium_lib_core/common/command.rb

@@ -43,6 +43,8 @@ module Commands
         hide_keyboard:              [:post, 'session/:session_id/appium/device/hide_keyboard'.freeze],
         press_keycode:              [:post, 'session/:session_id/appium/device/press_keycode'.freeze],
         long_press_keycode:         [:post, 'session/:session_id/appium/device/long_press_keycode'.freeze],
+        ## take_element_screenshot is for MJSONWP. W3C already has.
+        take_element_screenshot:    [:get,  'session/:session_id/element/:id/screenshot'.freeze],
         # keyevent is only for Selendroid
         keyevent:                   [:post, 'session/:session_id/appium/device/keyevent'.freeze],
         set_immediate_value:        [:post, 'session/:session_id/appium/element/:id/value'.freeze],

lib/appium_lib_core/common/device.rb

@@ -375,6 +375,16 @@ module Device
       #   @driver.switch_to_default_context
       #
 
+      # @!method take_element_screenshot(element, png_path)
+      # @param [Selenium::WebDriver::Element] element A element you'd like to take screenshot.
+      # @param [String] png_path A path to save the screenshot
+      # @return [File] Path to the screenshot.
+      #
+      # @example
+      #
+      #   @driver.take_element_screenshot(element, "fine_name.png")
+      #
+
       ####
       ## class << self
       ####
@@ -454,6 +464,19 @@ def hide_keyboard(close_key = nil, strategy = nil)
             end
           end
 
+          add_endpoint_method(:take_element_screenshot) do
+            def take_element_screenshot(element, png_path)
+              result = execute :take_element_screenshot, id: element.ref
+
+              extension = File.extname(png_path).downcase
+              if extension != '.png'
+                WebDriver.logger.warn 'name used for saved screenshot does not match file type. '\
+                                'It should end with .png extension'
+              end
+              File.open(png_path, 'wb') { |f| f << result.unpack('m')[0] }
+            end
+          end
+
           add_endpoint_method(:set_immediate_value) do
             def set_immediate_value(element, *value)
               keys = ::Selenium::WebDriver::Keys.encode(value)

test/functional/android/android/device_test.rb

@@ -280,6 +280,15 @@ def test_within_context
         assert_equal 'App', result.text
       end
 
+      def test_take_element_screenshot
+        e = @@core.wait { @@driver.find_element :accessibility_id, 'App' }
+        @@driver.take_element_screenshot(e, 'take_element_screenshot.png')
+
+        assert File.exist? 'take_element_screenshot.png'
+
+        File.delete 'take_element_screenshot.png'
+      end
+
       private
 
       def scroll_to(text)

test/unit/android/device_test.rb

@@ -51,6 +51,7 @@ def test_with_arg_definitions
                                             :keyevent,
                                             :press_keycode,
                                             :long_press_keycode,
+                                            :take_element_screenshot,
                                             :set_immediate_value,
                                             :replace_value,
                                             :push_file,
@@ -351,6 +352,15 @@ def test_long_press_keycode
         assert_requested(:post, "#{SESSION}/appium/device/long_press_keycode", times: 1)
       end
 
+      def test_take_element_screenshot
+        stub_request(:get, "#{SESSION}/element/id/screenshot")
+          .to_return(headers: HEADER, status: 200, body: { value: '' }.to_json)
+
+        @driver.take_element_screenshot ::Selenium::WebDriver::Element.new(@driver.send(:bridge), 'id'), 'sample.png'
+
+        assert_requested(:get, "#{SESSION}/element/id/screenshot", times: 1)
+      end
+
       def test_set_immediate_value
         stub_request(:post, "#{SESSION}/appium/element/id/value")
           .to_return(headers: HEADER, status: 200, body: { value: '' }.to_json)

test/unit/script/commands_test.rb

@@ -22,7 +22,7 @@ def test_get_all_command_path
 
     # depends on webdriver-version... (number of commands)
     def test_implemented_mjsonwp_commands
-      assert_equal 128, @c.implemented_mjsonwp_commands.length
+      assert_equal 129, @c.implemented_mjsonwp_commands.length
       assert_equal ['session/:session_id/contexts', [:get]], @c.implemented_mjsonwp_commands.first
 
       # pick up an arbitrary command
@@ -38,7 +38,7 @@ def test_implemented_w3c_commands
     end
 
     def test_implemented_core_commands
-      assert_equal 43, @c.implemented_core_commands.length
+      assert_equal 44, @c.implemented_core_commands.length
       assert_equal ['session/:session_id/contexts', [:get]], @c.implemented_core_commands.first
 
       # pick up an arbitrary command