MDL-71134 course: fix format get_output_classname

The get_output_classname method is used to invoke overridden output
components from course_formats. Now the method does not accept null
output names anymore, and it controls the format class is extending
the core one.

course/classes/course_format.php

@@ -33,6 +33,7 @@ use section_info;
 use context_course;
 use editsection_form;
 use moodle_exception;
+use coding_exception;
 use moodle_url;
 use lang_string;
 use completion_info;
@@ -1074,16 +1075,24 @@ abstract class course_format {
     /**
      * Returns instance of output compornent used by this plugin
      *
+     * @throws coding_exception if the format class does not extends the original core one.
      * @param string $outputname the element to render (section, activity...)
      * @return string the output component classname
      */
-    public function get_output_classname(?string $outputname): string {
+    public function get_output_classname(string $outputname): string {
+        // The core output class.
+        $baseclass = "core_course\\output\\$outputname";
+        // Check if there is a specific format class.
         $component = 'format_'. $this->get_format();
         $outputclass = "$component\\output\\$outputname";
         if (class_exists($outputclass)) {
+            // Check that the outputclass is a subclass of the base class.
+            if (!is_subclass_of($outputclass, $baseclass)) {
+                throw new coding_exception("The \"$outputclass\" must extend \"$baseclass\"");
+            }
             return $outputclass;
         }
-        return "core_course\\output\\$outputname";
+        return $baseclass;
     }
 
     /**

course/tests/courseformat_test.php

@@ -24,11 +24,19 @@
 
 defined('MOODLE_INTERNAL') || die();
 
-global $CFG;
-require_once($CFG->dirroot . '/course/lib.php');
-require_once($CFG->dirroot . '/course/tests/fixtures/format_theunittest.php');
+class courseformat_test extends advanced_testcase {
+
+    /**
+     * Setup to ensure that fixtures are loaded.
+     */
+    public static function setupBeforeClass(): void {
+        global $CFG;
+        require_once($CFG->dirroot . '/course/lib.php');
+        require_once($CFG->dirroot . '/course/tests/fixtures/format_theunittest.php');
+        require_once($CFG->dirroot . '/course/tests/fixtures/format_theunittest_output_course_format_state.php');
+        require_once($CFG->dirroot . '/course/tests/fixtures/format_theunittest_output_course_format_invalidoutput.php');
+    }
 
-class core_course_courseformat_testcase extends advanced_testcase {
     public function test_available_hook() {
         global $DB;
         $this->resetAfterTest();
@@ -200,6 +208,53 @@ class core_course_courseformat_testcase extends advanced_testcase {
         $this->assertNotEmpty($format->get_view_url(1, ['navigation' => 1]));
         $this->assertNotEmpty($format->get_view_url(0, ['navigation' => 1]));
     }
+
+    /**
+     * Test for get_output_classname method.
+     *
+     * @dataProvider get_output_classname_provider
+     * @param string $find the class to find
+     * @param string $result the expected result classname
+     * @param bool $exception if the method will raise an exception
+     */
+    public function test_get_output_classname($find, $result, $exception) {
+        $this->resetAfterTest();
+
+        $course = $this->getDataGenerator()->create_course(['format' => 'theunittest']);
+        $courseformat = course_get_format($course);
+
+        if ($exception) {
+            $this->expectException(coding_exception::class);
+        }
+
+        $courseclass = $courseformat->get_output_classname($find);
+        $this->assertEquals($result, $courseclass);
+    }
+
+    /**
+     * Data provider for test_get_output_classname.
+     *
+     * @return array the testing scenarios
+     */
+    public function get_output_classname_provider(): array {
+        return [
+            'overridden class' => [
+                'find' => 'course_format\\state',
+                'result' => 'format_theunittest\\output\\course_format\\state',
+                'exception' => false,
+            ],
+            'original class' => [
+                'find' => 'section_format\\state',
+                'result' => 'core_course\\output\\section_format\\state',
+                'exception' => false,
+            ],
+            'invalid overridden class' => [
+                'find' => 'course_format\\invalidoutput',
+                'result' => '',
+                'exception' => true,
+            ],
+        ];
+    }
 }
 
 /**

course/tests/fixtures/format_theunittest_output_course_format_invalidoutput.php

@@ -0,0 +1,43 @@
+<?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/>.
+
+namespace format_theunittest\output\course_format;
+
+use renderable;
+use templatable;
+use stdClass;
+
+/**
+ * Fixture for an invalid output for testing get_output_classname.
+ *
+ * @package    core_course
+ * @copyright  2021 Ferran Recio ([email protected])
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+class invalidoutput implements renderable, templatable {
+
+    /**
+     * Export some data.
+     *
+     * @param renderer_base $output typically, the renderer that's calling this function
+     * @return stdClass data context for a mustache template
+     */
+    public function export_for_template(\renderer_base $output): stdClass {
+        return (object)[
+            'something' => 'invalid',
+        ];
+    }
+}