MDL-83977 qbank: Migrate unused question categories

Previously, question categories which contained only questions with no
usages were deleted during migration to mod_qbank.

The intention is that hidden questions with no usages should be deleted,
then any categories which are now empty should be deleted rather than
migrated. The case of questions in non-hidden states with no usages was
not covered in the unit tests, and these were being deleted too.

This change will specifically check if a category is empty, rather than
checking question usage, before deletion.

mod/qbank/classes/task/transfer_question_categories.php

@@ -82,7 +82,7 @@ public function execute() {
             $subcategories = array_reverse(\sort_categories_by_tree($subcategories, $oldtopcategory->id));
             foreach ($subcategories as $subcategory) {
                 \qbank_managecategories\helper::question_remove_stale_questions_from_category($subcategory->id);
-                if (!question_category_in_use($subcategory->id)) {
+                if (!$DB->record_exists('question_bank_entries', ['questioncategoryid' => $subcategory->id])) {
                     question_category_delete_safe($subcategory);
                 }
             }

mod/qbank/tests/transfer_question_categories_test.php

@@ -55,6 +55,9 @@ final class transfer_question_categories_test extends \advanced_testcase {
     /** @var \core\context\module  test quiz mod context */
     private \core\context\module $quizcontext;
 
+    /** @var \core\context\course Course context with used and unused questions. */
+    private \core\context\course $usedunusedcontext;
+
     /** @var stdClass[] test stale questions */
     private array $stalequestions;
 
@@ -236,6 +239,22 @@ protected function setup_pre_install_data(): void {
         $question2 = $questiongenerator->create_question('shortanswer', null, ['category' => $quizchildcat1->id]);
         quiz_add_quiz_question($question1->id, $quiz, 1);
         quiz_add_quiz_question($question2->id, $quiz, 1);
+
+        // Set up a course with three categories
+        // - One contains questions including 1 that is used in a quiz.
+        // - One contains questions that are not used anywhere, but are in "ready" state.
+        // - One contains no questions.
+        $course = self::getDataGenerator()->create_course(['shortname' => 'Used-Unused-Empty']);
+        $this->usedunusedcontext = context_course::instance($course->id);
+        $usedcategory = $this->create_question_category(name: 'Used Question Cat', contextid: $this->usedunusedcontext->id);
+        $unusedcategory = $this->create_question_category('Unused Question Cat', $this->usedunusedcontext->id);
+        $emptycategory = $this->create_question_category('Empty Cat', $this->usedunusedcontext->id);
+        $question1 = $questiongenerator->create_question('shortanswer', null, ['category' => $usedcategory->id]);
+        $question2 = $questiongenerator->create_question('shortanswer', null, ['category' => $usedcategory->id]);
+        $question3 = $questiongenerator->create_question('shortanswer', null, ['category' => $unusedcategory->id]);
+        $question4 = $questiongenerator->create_question('shortanswer', null, ['category' => $unusedcategory->id]);
+        $quiz = $quizgenerator->create_instance(['course' => $course->id, 'grade' => 100.0, 'sumgrades' => 2, 'layout' => '1,0']);
+        quiz_add_quiz_question($question1->id, $quiz, 1);
     }
 
     /**
@@ -304,6 +323,19 @@ public function test_setup_pre_install_data(): void {
         $this->assertEquals($childcat2->id, $grandchildcat1->parent);
         $questionids = $this->get_question_data(array_map(static fn($cat) => $cat->id, $questioncats));
         $this->assertCount(5, $questionids);
+
+        // Make sure the "Used-Unused-Empty" course has 4 question categories (including 'top') with 0, 2, 2, and 0
+        // questions respectively.
+        $questioncats = $DB->get_records('question_categories', ['contextid' => $this->usedunusedcontext->id], 'id ASC');
+        $this->assertCount(4, $questioncats);
+        $topcat = reset($questioncats);
+        $this->assertEmpty($this->get_question_data([$topcat->id]));
+        $usedcat = next($questioncats);
+        $this->assertCount(2, $this->get_question_data([$usedcat->id]));
+        $unusedcat = next($questioncats);
+        $this->assertCount(2, $this->get_question_data([$unusedcat->id]));
+        $emptycat = next($questioncats);
+        $this->assertCount(0, $this->get_question_data([$emptycat->id]));
     }
 
     /**
@@ -434,5 +466,30 @@ public function test_qbank_install(): void {
         $this->assertCount(3, $quizcategories);
         $questions = $this->get_question_data(array_map(static fn($cat) => $cat->id, $quizcategories));
         $this->assertCount(2, $questions);
+
+        // Used-Unused-Empty checks.
+        // The empty category should have been removed. The other categories should both have been migrated to a qbank module,
+        // with all of their questions.
+        $usedunusedmodinfo = get_fast_modinfo($this->usedunusedcontext->instanceid);
+        $usedunusedcourse = $usedunusedmodinfo->get_course();
+        $usedunusedqbanks = $usedunusedmodinfo->get_instances_of('qbank');
+        $usedunusedqbank = reset($usedunusedqbanks);
+        $this->assertEquals("{$usedunusedcourse->shortname} shared question bank", $usedunusedqbank->name);
+
+        // We should now only have 3 categories. Top, used and unused.
+        $usedunusedcats = $DB->get_records(
+            'question_categories',
+            ['contextid' => $usedunusedqbank->context->id],
+            fields: 'name, id',
+        );
+        $this->assertCount(3, $usedunusedcats);
+        $this->assertTrue(array_key_exists('top', $usedunusedcats));
+        $this->assertTrue(array_key_exists('Used Question Cat', $usedunusedcats));
+        $this->assertTrue(array_key_exists('Unused Question Cat', $usedunusedcats));
+        $this->assertFalse(array_key_exists('Empty Question Cat', $usedunusedcats));
+
+        $this->assertEmpty($this->get_question_data([$usedunusedcats['top']->id]));
+        $this->assertCount(2, $this->get_question_data([$usedunusedcats['Used Question Cat']->id]));
+        $this->assertCount(2, $this->get_question_data([$usedunusedcats['Unused Question Cat']->id]));
     }
 }