diff --git a/question/classes/local/bank/context_to_string_translator.php b/question/classes/local/bank/context_to_string_translator.php
index 278db11481b..1e2d53c8be6 100644
--- a/question/classes/local/bank/context_to_string_translator.php
+++ b/question/classes/local/bank/context_to_string_translator.php
@@ -68,6 +68,7 @@ class context_to_string_translator {
     protected function generate_context_to_string_array($contexts) {
         if (!$this->contexttostringarray) {
             $catno = 1;
+            /** @var \context $context */
             foreach ($contexts as $context) {
                 switch ($context->contextlevel) {
                     case CONTEXT_MODULE :
@@ -83,6 +84,11 @@ class context_to_string_translator {
                     case CONTEXT_SYSTEM :
                         $contextstring = 'system';
                         break;
+                    default:
+                        throw new \coding_exception('Unexpected context level ' .
+                                \context_helper::get_level_name($context->contextlevel) . ' for context ' .
+                                $context->id . ' in generate_context_to_string_array. ' .
+                                'Questions can never exist in this type of context.');
                 }
                 $this->contexttostringarray[$context->id] = $contextstring;
             }
diff --git a/question/tests/local/bank/context_to_string_translator_test.php b/question/tests/local/bank/context_to_string_translator_test.php
new file mode 100644
index 00000000000..d761861d752
--- /dev/null
+++ b/question/tests/local/bank/context_to_string_translator_test.php
@@ -0,0 +1,79 @@
+<?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 core_question\local\bank;
+
+use context_course;
+use context_coursecat;
+use context_module;
+use context_system;
+use context_user;
+
+/**
+ * Unit tests for the context_to_string_translator class.
+ *
+ * @package   core_question
+ * @category  test
+ * @copyright 2023 the Open University
+ * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ * @covers \core_question\local\bank\context_to_string_translator
+ */
+class context_to_string_translator_test extends \advanced_testcase {
+
+    public function test_context_to_string_translator_test_good_case() {
+        $this->resetAfterTest();
+        $generator = $this->getDataGenerator();
+
+        // Generate a quiz in a course in a category.
+        $systemcontext = context_system::instance();
+
+        $category = $generator->create_category();
+        $categorycontext = context_coursecat::instance($category->id);
+
+        $course = $generator->create_course(['category' => $category->id]);
+        $coursecontext = context_course::instance($course->id);
+
+        $quiz = $generator->create_module('quiz', ['course' => $course->id]);
+        $quizcontext = context_module::instance($quiz->cmid);
+
+        // Create the context_to_string_translator.
+        $translator = new context_to_string_translator((new question_edit_contexts($quizcontext))->all());
+
+        // Verify its behaviour.
+        $this->assertEquals('module', $translator->context_to_string($quizcontext->id));
+        $this->assertEquals($quizcontext->id, $translator->string_to_context('module'));
+
+        $this->assertEquals('course', $translator->context_to_string($coursecontext->id));
+        $this->assertEquals($coursecontext->id, $translator->string_to_context('course'));
+
+        $this->assertEquals('cat1', $translator->context_to_string($categorycontext->id));
+        $this->assertEquals($categorycontext->id, $translator->string_to_context('cat1'));
+
+        $this->assertEquals('system', $translator->context_to_string($systemcontext->id));
+        $this->assertEquals($systemcontext->id, $translator->string_to_context('system'));
+    }
+
+    public function test_context_to_string_translator_throws_exception_with_bad_context() {
+        global $USER;
+        $this->resetAfterTest();
+        $this->setAdminUser();
+        $context = context_user::instance($USER->id);
+        $this->expectExceptionMessage('Unexpected context level User for context ' .
+                $context->id . ' in generate_context_to_string_array. ' .
+                'Questions can never exist in this type of context.');
+        new context_to_string_translator((new question_edit_contexts($context))->all());
+    }
+}