CSS Motion Path: Web Platform tests for longhand parsing

third_party/WebKit/LayoutTests/external/wpt/css/motion-1/resources/testcommon.js

+'use strict';

[suzyh_UTC10 (ex-contributor), 2017/05/22 01:46:20]

My comments on https://codereview.chromium.org/2882153004 for the parsing
testcommon file apply here too, as well as the suggestion to group these tests
under a parsing subdirectory to add structure to the test suite.

+
+function assert_valid_value(property, value) {
+    var stringifiedValue = JSON.stringify(value);
+
+    test(function(){
+        var div = document.createElement('div');
+        div.style[property] = value;
+        assert_not_equals(div.style[property], "");
+    }, "e.style['" + property + "'] = " + stringifiedValue + " should set the value");
+
+    test(function(){
+        var div = document.createElement('div');
+        div.style[property] = value;
+        assert_equals(div.style[property], value);
+    }, "Serialization should round-trip after setting e.style['" + property + "'] = " + stringifiedValue);
+}
+
+function assert_invalid_value(property, value) {
+    var stringifiedValue = JSON.stringify(value);
+
+    test(function(){
+        var div = document.createElement('div');
+        div.style[property] = value;
+        assert_equals(div.style[property], "");
+    }, "e.style['" + property + "'] = " + stringifiedValue + " should not set the value");
+}