Introducing an element selector for tests.

There are a number of ways for selecting an element in a tested html page, and those involve
injecting javascript. This class is intended to be used for abstracting this js generation
to diminish the proliferation of ad-hoc code.

Bug: None
Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: Ifbe1ba8be509dfe3ab02ff8b7ddca6cefc3761ff
Reviewed-on: https://chromium-review.googlesource.com/1118160
Commit-Queue: Eric Noyau <noyau@chromium.org>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#571069}

ios/web/public/test/BUILD.gn

@@ -28,6 +28,8 @@ source_set("test") {
   allow_circular_includes_from = [ "//ios/web/test:test_support" ]
 
   sources = [
+    "element_selector.h",
+    "element_selector.mm",
     "error_test_util.h",
     "error_test_util.mm",
     "js_test_util.h",

ios/web/public/test/element_selector.h

+// Copyright 2018 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef IOS_WEB_PUBLIC_TEST_ELEMENT_SELECTOR_H_
+#define IOS_WEB_PUBLIC_TEST_ELEMENT_SELECTOR_H_
+
+#include <string>
+
+namespace web {
+namespace test {
+
+// An ElementSelector is used to generate the proper javascript to retrieve an
+// element on a web page. It encapsulates the various means of finding an
+// element and is intended to be passed around.
+class ElementSelector {
+ public:
+  // Returns an ElementSelector to retrieve an element by ID.
+  static const ElementSelector ElementSelectorId(const std::string element_id);
+
+  // Returns an ElementSelector to retrieve an element by a CSS selector.
+  static const ElementSelector ElementSelectorCss(
+      const std::string css_selector);
+
+  // Returns an ElementSelector to retrieve an element by a xpath query.
+  static const ElementSelector ElementSelectorXPath(
+      const std::string xpath_selector);
+
+  ElementSelector(const ElementSelector& that) = default;
+  ElementSelector(ElementSelector&& that) = default;
+  ~ElementSelector() = default;
+
+  // Returns the javascript to invoke on a page to retrieve the element.
+  const std::string GetSelectorScript() const;
+
+  // Return a human readable description of the query.
+  const std::string GetSelectorDescription() const;
+
+ private:
+  ElementSelector(const std::string&& script, const std::string&& description);
+
+  const std::string script_;
+  const std::string description_;
+};
+
+}  // namespace test
+}  // namespace web
+
+#endif  // IOS_WEB_PUBLIC_TEST_ELEMENT_SELECTOR_H_

ios/web/public/test/element_selector.mm

+// Copyright 2018 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "ios/web/public/test/element_selector.h"
+
+#include "base/strings/stringprintf.h"
+
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
+namespace web {
+namespace test {
+
+// Static.
+const ElementSelector ElementSelector::ElementSelectorId(
+    const std::string element_id) {
+  return ElementSelector(
+      base::StringPrintf("document.getElementById('%s')", element_id.c_str()),
+      base::StringPrintf("with ID '%s')", element_id.c_str()));
+}
+
+// Static.
+const ElementSelector ElementSelector::ElementSelectorCss(
+    const std::string css_selector) {
+  const std::string script(base::StringPrintf("document.querySelector(\"%s\")",
+                                              css_selector.c_str()));
+  const std::string description(
+      base::StringPrintf("with CSS selector '%s')", css_selector.c_str()));
+  return ElementSelector(std::move(script), std::move(description));
+}
+
+// Static.
+const ElementSelector ElementSelector::ElementSelectorXPath(
+    const std::string xpath_selector) {
+  const std::string script(base::StringPrintf(
+      "document.evaluate(`%s`, document, "
+      "null,XPathResult.FIRST_ORDERED_NODE_TYPE, null).singleNodeValue",
+      xpath_selector.c_str()));
+  const std::string description(
+      base::StringPrintf("with xpath '%s')", xpath_selector.c_str()));
+  return ElementSelector(std::move(script), std::move(description));
+}
+
+ElementSelector::ElementSelector(const std::string&& script,
+                                 const std::string&& description)
+    : script_(script), description_(description) {}
+
+const std::string ElementSelector::GetSelectorScript() const {
+  return script_;
+}
+const std::string ElementSelector::GetSelectorDescription() const {
+  return description_;
+}
+
+}  // namespace test
+}  // namespace web