test: tweak test case (#245)

Author: KazuCocoa

test/functional/ios/ios/device_test.rb

@@ -119,7 +119,7 @@ def test_context_related
         assert_equal 'NATIVE_APP', @@driver.current_context
 
         @@driver.back # go to top
-        @@core.wait { assert @@driver.available_contexts.size == 2 }
+        @@core.wait { assert [1, 2].member? @@driver.available_contexts.size }
       end
 
       def test_app_string

test/functional/ios/ios/mobile_commands_test.rb

@@ -127,6 +127,9 @@ def test_source
         assert !json.empty?
         assert !xml.empty?
         assert !description.empty? # get a vanilla xcuitest description data
+
+        xml2 = @driver.execute_script 'mobile: source', { format: :xml, excludedAttributes: ['visible'] }
+        assert !xml2.empty?
       end
 
       def test_device_info