diff --git a/tests/external/favourite_package_test.php b/tests/external/favourite_package_test.php
index d94b6727..6001d553 100644
--- a/tests/external/favourite_package_test.php
+++ b/tests/external/favourite_package_test.php
@@ -45,7 +45,7 @@
  * @copyright  2024 TU Berlin, innoCampus {@link https://www.questionpy.org}
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
-class favourite_package_test extends \externallib_advanced_testcase {
+final class favourite_package_test extends \externallib_advanced_testcase {
     /**
      * This method is called before each test.
      */
diff --git a/tests/external/get_tags_test.php b/tests/external/get_tags_test.php
index d7db4301..9bc0bda2 100644
--- a/tests/external/get_tags_test.php
+++ b/tests/external/get_tags_test.php
@@ -44,7 +44,7 @@
  * @copyright  2024 TU Berlin, innoCampus {@link https://www.questionpy.org}
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
-class get_tags_test extends \externallib_advanced_testcase {
+final class get_tags_test extends \externallib_advanced_testcase {
     /**
      * Test that the user needs to be logged in.
      *
diff --git a/tests/external/search_packages_test.php b/tests/external/search_packages_test.php
index 19332492..e5061d6e 100644
--- a/tests/external/search_packages_test.php
+++ b/tests/external/search_packages_test.php
@@ -47,7 +47,7 @@
  * @copyright  2023 TU Berlin, innoCampus {@link https://www.questionpy.org}
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
-class search_packages_test extends \externallib_advanced_testcase {
+final class search_packages_test extends \externallib_advanced_testcase {
     /**
      * This method is called before each test.
      */
@@ -839,7 +839,7 @@ public function test_favourites_are_not_shared_across_users(): void {
      * @return void
      * @throws moodle_exception
      */
-    public function test_search_with_tags() {
+    public function test_search_with_tags(): void {
         global $DB;
 
         package_provider(['namespace' => 'ns1', 'tags' => ['a']])->store();
diff --git a/tests/form/elements/element_html_test.php b/tests/form/elements/element_html_test.php
index 7dbf23f5..7ff5ab79 100644
--- a/tests/form/elements/element_html_test.php
+++ b/tests/form/elements/element_html_test.php
@@ -32,7 +32,7 @@
  * @copyright  2022 TU Berlin, innoCampus {@link https://www.questionpy.org}
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
-class element_html_test extends \advanced_testcase {
+final class element_html_test extends \advanced_testcase {
     /**
      * Implements a snapshot testing approach similar to that of {@link https://jestjs.io/docs/snapshot-testing Jest}.
      *
diff --git a/tests/form/elements/element_json_test.php b/tests/form/elements/element_json_test.php
index a7094a95..706f3b3e 100644
--- a/tests/form/elements/element_json_test.php
+++ b/tests/form/elements/element_json_test.php
@@ -31,7 +31,7 @@
  * @copyright  2022 TU Berlin, innoCampus {@link https://www.questionpy.org}
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
-class element_json_test extends \advanced_testcase {
+final class element_json_test extends \advanced_testcase {
     /**
      * Serializes values and compares resulting JSON to an expected file.
      *
diff --git a/tests/http_response_container_test.php b/tests/http_response_container_test.php
index 3ddbee71..7025a8ae 100644
--- a/tests/http_response_container_test.php
+++ b/tests/http_response_container_test.php
@@ -26,7 +26,7 @@
  * @copyright  2022 Jan Britz, TU Berlin, innoCampus - www.questionpy.org
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
-class http_response_container_test extends \advanced_testcase {
+final class http_response_container_test extends \advanced_testcase {
     /**
      * Tests the function get_data with json.
      *
@@ -59,7 +59,7 @@ public function test_get_data_with_json(): void {
      * @return void
      * @throws moodle_exception
      */
-    public function test_get_data_not_json() {
+    public function test_get_data_not_json(): void {
         $code = 200;
         $data = 'This is not a json.';
 
diff --git a/tests/last_used_service_test.php b/tests/last_used_service_test.php
index 8d4ceb3a..bf98e82b 100644
--- a/tests/last_used_service_test.php
+++ b/tests/last_used_service_test.php
@@ -25,14 +25,14 @@
  * @copyright  2024 Jan Britz, TU Berlin, innoCampus - www.questionpy.org
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
-class last_used_service_test extends \advanced_testcase {
+final class last_used_service_test extends \advanced_testcase {
     /**
      * Tests {@see last_used_service::add()} create correct timestamp.
      *
      * @throws moodle_exception
      * @covers \qtype_questionpy\last_used_service::add
      */
-    public function test_add_creates_entry() {
+    public function test_add_creates_entry(): void {
         global $DB;
         $this->resetAfterTest();
 
@@ -53,7 +53,7 @@ public function test_add_creates_entry() {
      * @throws moodle_exception
      * @covers \qtype_questionpy\last_used_service::add
      */
-    public function test_add_updates_timestamp_if_package_was_already_used() {
+    public function test_add_updates_timestamp_if_package_was_already_used(): void {
         global $DB;
         $this->resetAfterTest();
 
@@ -81,7 +81,7 @@ public function test_add_updates_timestamp_if_package_was_already_used() {
      * @throws moodle_exception
      * @covers \qtype_questionpy\last_used_service::add
      */
-    public function test_add_inserts_entries_if_packages_differ() {
+    public function test_add_inserts_entries_if_packages_differ(): void {
         global $DB;
         $this->resetAfterTest();
 
@@ -107,7 +107,7 @@ public function test_add_inserts_entries_if_packages_differ() {
      * @throws moodle_exception
      * @covers \qtype_questionpy\last_used_service::add
      */
-    public function test_add_inserts_entries_if_contexts_differ() {
+    public function test_add_inserts_entries_if_contexts_differ(): void {
         global $DB;
         $this->resetAfterTest();
 
@@ -133,7 +133,7 @@ public function test_add_inserts_entries_if_contexts_differ() {
      * @throws moodle_exception
      * @covers \qtype_questionpy\last_used_service::add
      */
-    public function test_add_inserts_entries_if_packages_and_contexts_differ() {
+    public function test_add_inserts_entries_if_packages_and_contexts_differ(): void {
         global $DB;
         $this->resetAfterTest();
 
@@ -175,7 +175,7 @@ public static function context_count_provider(): array {
      * @dataProvider context_count_provider
      * @covers \qtype_questionpy\last_used_service::remove_by_package
      */
-    public function test_remove_by_package_removes_the_entries(int $contexts) {
+    public function test_remove_by_package_removes_the_entries(int $contexts): void {
         global $DB;
         $this->resetAfterTest();
 
@@ -197,7 +197,7 @@ public function test_remove_by_package_removes_the_entries(int $contexts) {
      * @throws moodle_exception
      * @covers \qtype_questionpy\last_used_service::remove_by_package
      */
-    public function test_remove_by_package_only_removes_the_given_package() {
+    public function test_remove_by_package_only_removes_the_given_package(): void {
         global $DB;
         $this->resetAfterTest();
 
diff --git a/tests/localizer_test.php b/tests/localizer_test.php
index 1e9ea539..8e8603a2 100644
--- a/tests/localizer_test.php
+++ b/tests/localizer_test.php
@@ -23,7 +23,7 @@
  * @copyright  2022 Jan Britz, TU Berlin, innoCampus - www.questionpy.org
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
-class localizer_test extends \advanced_testcase {
+final class localizer_test extends \advanced_testcase {
     /**
      * Test the default of the function get_preferred_language.
      *
diff --git a/tests/package/package_base_test.php b/tests/package/package_base_test.php
index 504e65ea..dd818008 100644
--- a/tests/package/package_base_test.php
+++ b/tests/package/package_base_test.php
@@ -23,7 +23,7 @@
  * @copyright  2023 Jan Britz, TU Berlin, innoCampus - www.questionpy.org
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
-class package_base_test extends \advanced_testcase {
+final class package_base_test extends \advanced_testcase {
     /**
      * Tests the method get_localized_name.
      *
diff --git a/tests/package/package_raw_test.php b/tests/package/package_raw_test.php
index f56f577a..b4bed6ac 100644
--- a/tests/package/package_raw_test.php
+++ b/tests/package/package_raw_test.php
@@ -31,7 +31,7 @@
  * @copyright  2023 Jan Britz, TU Berlin, innoCampus - www.questionpy.org
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
-class package_raw_test extends \advanced_testcase {
+final class package_raw_test extends \advanced_testcase {
     /**
      * Provides valid package data.
      *
@@ -138,7 +138,7 @@ public function test_from_array($packagedata): void {
      * @return void
      * @throws moodle_exception
      */
-    public function test_faulty_from_array() {
+    public function test_faulty_from_array(): void {
         $this->expectException(moodle_exception::class);
         $faulty = ['faulty' => 'hash'];
         array_converter::from_array(package_raw::class, $faulty);
@@ -154,7 +154,7 @@ public function test_faulty_from_array() {
      * @return void
      * @throws moodle_exception
      */
-    public function test_store_package($packagedata) {
+    public function test_store_package($packagedata): void {
         global $DB;
         $this->resetAfterTest();
 
@@ -219,7 +219,7 @@ public function test_store_package($packagedata) {
      * @return void
      * @throws moodle_exception
      */
-    public function test_store_package_twice() {
+    public function test_store_package_twice(): void {
         global $DB;
         $this->resetAfterTest();
 
@@ -241,7 +241,7 @@ public function test_store_package_twice() {
      * @return void
      * @throws moodle_exception
      */
-    public function test_store_already_existing_package_with_different_hash_throws() {
+    public function test_store_already_existing_package_with_different_hash_throws(): void {
         $this->resetAfterTest();
         $this->expectException(moodle_exception::class);
         $this->expectExceptionMessage('A package with the same version but different hash already exists.');
@@ -261,7 +261,7 @@ public function test_store_already_existing_package_with_different_hash_throws()
      * @return void
      * @throws moodle_exception
      */
-    public function test_store_different_versions_of_a_package() {
+    public function test_store_different_versions_of_a_package(): void {
         global $DB;
         $this->resetAfterTest();
 
diff --git a/tests/package/package_test.php b/tests/package/package_test.php
index a408a890..bb8cc493 100644
--- a/tests/package/package_test.php
+++ b/tests/package/package_test.php
@@ -30,7 +30,7 @@
  * @copyright  2022 Jan Britz, TU Berlin, innoCampus - www.questionpy.org
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
-class package_test extends \advanced_testcase {
+final class package_test extends \advanced_testcase {
     /**
      * Tests the method get_by_version.
      *
@@ -38,7 +38,7 @@ class package_test extends \advanced_testcase {
      * @return void
      * @throws moodle_exception
      */
-    public function test_get_by_version() {
+    public function test_get_by_version(): void {
         $this->resetAfterTest();
 
         // Store a package.
@@ -79,7 +79,7 @@ private function assert_records_count(int $pkgversion, int $package, int $langua
      * @return void
      * @throws moodle_exception
      */
-    public function test_delete() {
+    public function test_delete(): void {
         $this->resetAfterTest();
 
         // Store a package.
@@ -99,7 +99,7 @@ public function test_delete() {
      * @return void
      * @throws moodle_exception
      */
-    public function test_delete_with_multiple_versions() {
+    public function test_delete_with_multiple_versions(): void {
         $this->resetAfterTest();
 
         // Store two versions of the same package.
@@ -120,7 +120,7 @@ public function test_delete_with_multiple_versions() {
      * @return void
      * @throws moodle_exception
      */
-    public function test_delete_with_multiple_packages() {
+    public function test_delete_with_multiple_packages(): void {
         $this->resetAfterTest();
 
         // Store two packages.
@@ -144,7 +144,7 @@ public function test_delete_with_multiple_packages() {
      * @covers \qtype_questionpy\package::equals
      * @return void
      */
-    public function test_difference_from() {
+    public function test_difference_from(): void {
         $package1 = new package(0, 'shortname', 'namespace', [], 'type', 'author', 'url', ['en', 'de']);
         $package2 = new package(1, 'shortname', 'namespace', [], 'type', 'author', 'url', ['de', 'en']);
 
diff --git a/tests/package/package_version_test.php b/tests/package/package_version_test.php
index e59cfdcc..95434f67 100644
--- a/tests/package/package_version_test.php
+++ b/tests/package/package_version_test.php
@@ -31,14 +31,14 @@
  * @copyright  2023 Jan Britz, TU Berlin, innoCampus - www.questionpy.org
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
-class package_version_test extends \advanced_testcase {
+final class package_version_test extends \advanced_testcase {
     /**
      * Tests the get_by_id method.
      *
      * @covers \package_version::get_by_id
      * @throws moodle_exception
      */
-    public function test_get_by_id() {
+    public function test_get_by_id(): void {
         $this->resetAfterTest();
 
         // Store a package.
@@ -59,7 +59,7 @@ public function test_get_by_id() {
      * @depends test_get_by_id
      * @throws moodle_exception
      */
-    public function test_get_by_hash() {
+    public function test_get_by_hash(): void {
         $this->resetAfterTest();
 
         // Store a package.
@@ -80,7 +80,7 @@ public function test_get_by_hash() {
      * @depends test_get_by_id
      * @throws moodle_exception
      */
-    public function test_delete() {
+    public function test_delete(): void {
         global $DB;
         $this->resetAfterTest();
 
@@ -105,7 +105,7 @@ public function test_delete() {
      * @depends test_get_by_id
      * @throws moodle_exception
      */
-    public function test_delete_where_multiple_versions_exist() {
+    public function test_delete_where_multiple_versions_exist(): void {
         global $DB;
         $this->resetAfterTest();
 
diff --git a/tests/question_service_test.php b/tests/question_service_test.php
index db0fefcc..639f4169 100644
--- a/tests/question_service_test.php
+++ b/tests/question_service_test.php
@@ -33,7 +33,7 @@
  * @copyright  2022 TU Berlin, innoCampus {@link https://www.questionpy.org}
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
-class question_service_test extends \advanced_testcase {
+final class question_service_test extends \advanced_testcase {
     /** @var api */
     private api $api;
 
@@ -61,7 +61,7 @@ protected function setUp(): void {
      * @throws moodle_exception
      * @covers \qtype_questionpy\question_service::get_question
      */
-    public function test_get_question_should_load_package_and_state() {
+    public function test_get_question_should_load_package_and_state(): void {
         $this->resetAfterTest();
 
         $package = package_provider();
@@ -88,7 +88,7 @@ public function test_get_question_should_load_package_and_state() {
      * @throws moodle_exception
      * @covers \qtype_questionpy\question_service::get_question
      */
-    public function test_get_question_should_return_empty_object_when_no_record() {
+    public function test_get_question_should_return_empty_object_when_no_record(): void {
         $this->assertEquals(new stdClass(), $this->questionservice->get_question(42));
     }
 
@@ -100,7 +100,7 @@ public function test_get_question_should_return_empty_object_when_no_record() {
      * @throws moodle_exception
      * @covers \qtype_questionpy\question_service::upsert_question
      */
-    public function test_upsert_question_should_update_existing_record_if_changed() {
+    public function test_upsert_question_should_update_existing_record_if_changed(): void {
         global $PAGE;
         $this->resetAfterTest();
 
@@ -142,7 +142,7 @@ public function test_upsert_question_should_update_existing_record_if_changed()
      * @throws dml_exception
      * @covers \qtype_questionpy\question_service::upsert_question
      */
-    public function test_upsert_question_should_do_nothing_if_unchanged() {
+    public function test_upsert_question_should_do_nothing_if_unchanged(): void {
         global $PAGE;
         $this->resetAfterTest();
 
@@ -182,7 +182,7 @@ public function test_upsert_question_should_do_nothing_if_unchanged() {
      * @throws dml_exception
      * @covers \qtype_questionpy\question_service::upsert_question
      */
-    public function test_upsert_question_should_insert_record() {
+    public function test_upsert_question_should_insert_record(): void {
         global $PAGE;
         $this->resetAfterTest();
 
@@ -218,7 +218,7 @@ public function test_upsert_question_should_insert_record() {
      * @throws dml_exception
      * @covers \qtype_questionpy\question_service::upsert_question
      */
-    public function test_upsert_question_should_throw_when_package_does_not_exist() {
+    public function test_upsert_question_should_throw_when_package_does_not_exist(): void {
         $hash = hash("sha256", rand());
 
         $this->expectException(moodle_exception::class);
@@ -242,7 +242,7 @@ public function test_upsert_question_should_throw_when_package_does_not_exist()
      * @throws dml_exception
      * @covers \qtype_questionpy\question_service::upsert_question
      */
-    public function test_upsert_question_should_add_package_to_last_used_table() {
+    public function test_upsert_question_should_add_package_to_last_used_table(): void {
         global $DB, $PAGE;
         $this->resetAfterTest();
 
@@ -285,7 +285,7 @@ public function test_upsert_question_should_add_package_to_last_used_table() {
      * @throws dml_exception
      * @covers \qtype_questionpy\question_service::upsert_question
      */
-    public function test_upsert_question_in_same_context_with_same_package_should_only_update_time_used_in_last_used_table() {
+    public function test_upsert_question_in_same_context_with_same_package_should_only_update_time_used_in_last_used_table(): void {
         global $DB, $PAGE;
         $this->resetAfterTest();
 
@@ -348,7 +348,7 @@ public function test_upsert_question_in_same_context_with_same_package_should_on
      * @throws moodle_exception
      * @covers \qtype_questionpy\question_service::upsert_question
      */
-    public function test_delete_question() {
+    public function test_delete_question(): void {
         $this->resetAfterTest();
 
         $package = package_provider();
diff --git a/tests/question_type_test.php b/tests/question_type_test.php
index 21e63455..d5854753 100644
--- a/tests/question_type_test.php
+++ b/tests/question_type_test.php
@@ -23,14 +23,14 @@
  * @copyright  2022 Martin Gauk, TU Berlin, innoCampus - www.questionpy.org
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
-class question_type_test extends \advanced_testcase {
+final class question_type_test extends \advanced_testcase {
     /**
      * Dummy Test (replace when we have real methods testing the question type).
      *
      * @coversNothing
      * @return void
      */
-    public function test_dummy() {
+    public function test_dummy(): void {
         $this->assertTrue(true);
     }
 }
diff --git a/tests/question_ui_metadata_extractor_test.php b/tests/question_ui_metadata_extractor_test.php
index 3fae7cba..f9b9904e 100644
--- a/tests/question_ui_metadata_extractor_test.php
+++ b/tests/question_ui_metadata_extractor_test.php
@@ -24,14 +24,14 @@
  * @copyright  2023 TU Berlin, innoCampus {@link https://www.questionpy.org}
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
-class question_ui_metadata_extractor_test extends \advanced_testcase {
+final class question_ui_metadata_extractor_test extends \advanced_testcase {
     /**
      * Tests that metadata is correctly extracted from the UI's input elements.
      *
      * @covers \qtype_questionpy\question_ui_metadata_extractor
      * @covers \qtype_questionpy\question_metadata
      */
-    public function test_should_extract_correct_metadata() {
+    public function test_should_extract_correct_metadata(): void {
         $input = file_get_contents(__DIR__ . "/question_uis/metadata.xhtml");
 
         $metadata = new question_ui_metadata_extractor($input);
diff --git a/tests/question_ui_renderer_test.php b/tests/question_ui_renderer_test.php
index d260a570..ebe75644 100644
--- a/tests/question_ui_renderer_test.php
+++ b/tests/question_ui_renderer_test.php
@@ -26,7 +26,7 @@
  * @copyright  2023 TU Berlin, innoCampus {@link https://www.questionpy.org}
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
-class question_ui_renderer_test extends \advanced_testcase {
+final class question_ui_renderer_test extends \advanced_testcase {
     /**
      * Asserts that two html strings are equal.
      *
@@ -57,7 +57,7 @@ private function assert_html_string_equals_html_string(string $expectedhtml, str
      * @throws coding_exception
      * @covers \qtype_questionpy\question_ui_renderer
      */
-    public function test_should_hide_inline_feedback() {
+    public function test_should_hide_inline_feedback(): void {
         $input = file_get_contents(__DIR__ . "/question_uis/feedbacks.xhtml");
 
         $qa = $this->createStub(\question_attempt::class);
@@ -82,7 +82,7 @@ public function test_should_hide_inline_feedback() {
      * @throws coding_exception
      * @covers \qtype_questionpy\question_ui_renderer
      */
-    public function test_should_show_inline_feedback() {
+    public function test_should_show_inline_feedback(): void {
         $input = file_get_contents(__DIR__ . "/question_uis/feedbacks.xhtml");
 
         $qa = $this->createStub(\question_attempt::class);
@@ -108,7 +108,7 @@ public function test_should_show_inline_feedback() {
      * @throws coding_exception
      * @covers \qtype_questionpy\question_ui_renderer
      */
-    public function test_should_mangle_names() {
+    public function test_should_mangle_names(): void {
         $input = file_get_contents(__DIR__ . "/question_uis/ids_and_names.xhtml");
 
         $qa = $this->createStub(\question_attempt::class);
@@ -152,7 +152,7 @@ public function test_should_mangle_names() {
      * @throws coding_exception
      * @covers \qtype_questionpy\question_ui_renderer
      */
-    public function test_should_shuffle_the_same_way_in_same_attempt() {
+    public function test_should_shuffle_the_same_way_in_same_attempt(): void {
         $input = file_get_contents(__DIR__ . "/question_uis/shuffle.xhtml");
         $qa = $this->createStub(\question_attempt::class);
         $qa->method("get_database_id")
@@ -172,7 +172,7 @@ public function test_should_shuffle_the_same_way_in_same_attempt() {
      * @throws coding_exception
      * @covers \qtype_questionpy\question_ui_renderer
      */
-    public function test_should_resolve_placeholders() {
+    public function test_should_resolve_placeholders(): void {
         $input = file_get_contents(__DIR__ . "/question_uis/placeholder.xhtml");
         $qa = $this->createStub(\question_attempt::class);
         $qa->method("get_database_id")
@@ -203,7 +203,7 @@ public function test_should_resolve_placeholders() {
      * @throws coding_exception
      * @covers \qtype_questionpy\question_ui_renderer
      */
-    public function test_should_remove_placeholders_when_no_corresponding_value() {
+    public function test_should_remove_placeholders_when_no_corresponding_value(): void {
         $input = file_get_contents(__DIR__ . "/question_uis/placeholder.xhtml");
         $qa = $this->createStub(\question_attempt::class);
         $qa->method("get_database_id")
@@ -230,7 +230,7 @@ public function test_should_remove_placeholders_when_no_corresponding_value() {
      * @throws coding_exception
      * @covers \qtype_questionpy\question_ui_renderer
      */
-    public function test_should_soften_validations() {
+    public function test_should_soften_validations(): void {
         $input = file_get_contents(__DIR__ . "/question_uis/validations.xhtml");
         $qa = $this->createStub(\question_attempt::class);
         $qa->method("get_database_id")
@@ -260,7 +260,7 @@ public function test_should_soften_validations() {
      * @throws coding_exception
      * @covers \qtype_questionpy\question_ui_renderer
      */
-    public function test_should_defuse_buttons() {
+    public function test_should_defuse_buttons(): void {
         $input = file_get_contents(__DIR__ . "/question_uis/buttons.xhtml");
         $qa = $this->createStub(\question_attempt::class);
         $qa->method("get_database_id")
@@ -288,7 +288,7 @@ public function test_should_defuse_buttons() {
      * @throws coding_exception
      * @covers \qtype_questionpy\question_ui_renderer
      */
-    public function test_should_remove_element_with_if_role_attribute() {
+    public function test_should_remove_element_with_if_role_attribute(): void {
         $input = file_get_contents(__DIR__ . "/question_uis/if-role.xhtml");
         $qa = $this->createStub(\question_attempt::class);
         $qa->method("get_database_id")
@@ -315,7 +315,7 @@ public function test_should_remove_element_with_if_role_attribute() {
      * @throws coding_exception
      * @covers \qtype_questionpy\question_ui_renderer
      */
-    public function test_should_not_remove_element_with_if_role_attribute() {
+    public function test_should_not_remove_element_with_if_role_attribute(): void {
         $input = file_get_contents(__DIR__ . "/question_uis/if-role.xhtml");
         $qa = $this->createStub(\question_attempt::class);
         $qa->method("get_database_id")
@@ -349,7 +349,7 @@ public function test_should_not_remove_element_with_if_role_attribute() {
      * @throws coding_exception
      * @covers \qtype_questionpy\question_ui_renderer
      */
-    public function test_should_format_floats_in_en() {
+    public function test_should_format_floats_in_en(): void {
         $input = file_get_contents(__DIR__ . "/question_uis/format-floats.xhtml");
         $qa = $this->createStub(\question_attempt::class);
         $qa->method("get_database_id")