Adding $shuffleSubcategories option in function getCategoryExerciseTree() by default is false so no change to the current algorythm to gather question. Adding new function in order to get the categories based in the question list. getCategoriesFromQuestionList() see BT#6934. No changes to the current exercise display.

main/exercice/testcategory.class.php

@@ -666,10 +666,10 @@ class Testcategory
      * Returns an array of question ids for each category
      * $categories[1][30] = 10, array with category id = 1 and question_id = 10
      * A question has "n" categories
-     * @param int exercise
+     * @param int $exerciseId
-     * @param array check question list
+     * @param array $check_in_question_list
-     * @param array
+     * @param array $categoriesAddedInExercise
-     * @param int
+     * @param int $courseId
      * @return array
 	 */
     static function getQuestionsByCat(
@@ -1130,7 +1130,9 @@ class Testcategory
      * @param int $exercise_id
      * @param int $course_id
      * @param string $order
+     * @param bool shuffle
      * @param bool $excludeCategoryWithNoQuestions
+     * @param bool $shuffleSubcategories
      * @return array
      */
     public function getCategoryExerciseTree(
@@ -1138,7 +1140,8 @@ class Testcategory
         $course_id,
         $order = null,
         $shuffle = false,
-        $excludeCategoryWithNoQuestions = true
+        $excludeCategoryWithNoQuestions = true,
+        $shuffleSubcategories = false
     ) {
         $table = Database::get_course_table(TABLE_QUIZ_REL_CATEGORY);
         $table_category = Database::get_course_table(TABLE_QUIZ_CATEGORY);
@@ -1149,7 +1152,6 @@ class Testcategory
             $sql .= "ORDER BY $order";
         }
         $categories = array();
-
         $result = Database::query($sql);
         if (Database::num_rows($result)) {
              while ($row = Database::fetch_array($result, 'ASSOC')) {
@@ -1160,7 +1162,29 @@ class Testcategory
                 }
                 $categories[$row['category_id']] = $row;
             }
+        }
+
+        // Shuffle sub categories.
+        if ($shuffleSubcategories) {
+            $categoriesByParent = array();
+            foreach ($categories as $cat)  {
+                $categoriesByParent[$cat['parent_id']][] = $cat;
+            }
+
+            if (!empty($categoriesByParent)) {
+                foreach ($categoriesByParent as &$categoryList) {
+                    ArrayClass::shuffle_assoc($categoryList);
+                }
+
+                $newCategoryList = array();
+                foreach ($categoriesByParent as $categoryListToOrder) {
+                    foreach ($categoryListToOrder as $categoryItem) {
+                        $newCategoryList[$categoryItem['iid']] = $categoryItem;
+                    }
+                }
+                $categories = $newCategoryList;
             }
+        }
 
         if ($shuffle) {
             ArrayClass::shuffle_assoc($categories);
@@ -1312,4 +1336,22 @@ class Testcategory
         $global = ($row['c_id'] == 0 ? true : false);
         return $global;
     }
+
+    /**
+     * @param array $questionList
+     * @param int $courseId
+     * @return array
+     */
+    public static function getCategoriesFromQuestionList($questionList, $courseId)
+    {
+        $categories = array();
+        foreach ($questionList as $questionId) {
+            $categoryList = self::getCategoryForQuestionWithCategoryData($questionId, $courseId);
+            foreach ($categoryList as $categoryData) {
+                $categoryData['name'] = $categoryData['title'];
+                $categories[$categoryData['iid']][] = $questionId;
+            }
+        }
+        return $categories;
+    }
 }