MDL-75887 behat: Add ability to set value regardless of the editor

Prior to this commit, the behat_form_editor integration was hard-coded
to use Atto.

This change allows other editors to be used to set editor values, and
breaks that hard bond. Following this change, any editor is able to
define a behat_editor_[name].php file defining a function which meets
the following signature:

  set_editor_value(string $editorid, string $value): void

Each editor is responsible for checking whether its own API is available
and calling any relevant functions to force the editor to set the
content.

Please note: Behat is unable to determine the current editor in use on
the page automatically.

lib/editor/atto/tests/behat/behat_editor_atto.php

@@ -28,6 +28,7 @@ use Behat\Behat\Hook\Scope\BeforeScenarioScope;
 // NOTE: no MOODLE_INTERNAL test here, this file may be required by behat before including /config.php.
 
 require_once(__DIR__ . '/../../../../behat/behat_base.php');
+require_once(__DIR__ . '/../../../../behat/classes/settable_editor.php');
 
 /**
  * Steps definitions to deal with the atto text editor
@@ -37,7 +38,30 @@ require_once(__DIR__ . '/../../../../behat/behat_base.php');
  * @copyright  2014 Damyon Wiese
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
-class behat_editor_atto extends behat_base {
+class behat_editor_atto extends behat_base implements \core_behat\settable_editor {
+
+    /**
+     * Set the value for the editor.
+     *
+     * @param string $editorid
+     * @param string $value
+     */
+    public function set_editor_value(string $editorid, string $value): void {
+        $js = <<<EOF
+            (function() {
+                const editableEditor = document.getElementById("${editorid}editable");
+                if (editableEditor && editableEditor.classList.contains('editor_atto_content')) {
+                    editableEditor.innerHTML = "${value}";
+                }
+                const editor = document.getElementById("${editorid}");
+                if (editor) {
+                    editor.value = "${value}";
+                }
+            })();
+        EOF;
+
+        $this->execute_script($js);
+    }
 
     /**
      * Select the text in an Atto field.

lib/editor/textarea/tests/behat/behat_editor_textarea.php

@@ -0,0 +1,48 @@
+<?php
+// This file is part of Moodle - http://moodle.org/
+//
+// Moodle is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Moodle is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
+
+/**
+ * Moodle textarea editor field.
+ *
+ * @package    core_form
+ * @category   test
+ * @copyright  2022 Andrew Lyons <andrew@nicols.co.uk>
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+
+require_once(__DIR__ . '/../../../../behat/behat_base.php');
+require_once(__DIR__ . '/../../../../behat/classes/settable_editor.php');
+
+class behat_editor_textarea extends behat_base implements \core_behat\settable_editor {
+
+    /**
+     * Set the value for the editor.
+     *
+     * @param string $editorid
+     * @param string $value
+     */
+    public function set_editor_value(string $editorid, string $value): void {
+        $js = <<<EOF
+            (function() {
+                const editor = document.getElementById("${editorid}");
+                if (editor && editor.tagName.toLowerCase() === 'textarea') {
+                    editor.value = "${value}";
+                }
+            })();
+        EOF;
+        $this->execute_script($js);
+    }
+}