diff --git a/lib/tests/classes/phpunit/data_provider_finished_subscriber.php b/lib/tests/classes/phpunit/data_provider_finished_subscriber.php
new file mode 100644
index 00000000000..162f11e5e05
--- /dev/null
+++ b/lib/tests/classes/phpunit/data_provider_finished_subscriber.php
@@ -0,0 +1,116 @@
+<?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\tests\phpunit;
+
+use PHPUnit\Event\Test\DataProviderMethodFinished;
+use PHPUnit\Event\Test\DataProviderMethodFinishedSubscriber;
+
+/**
+ * PHPUnit Event Subscriber for DataProviderMethodFinished event.
+ *
+ * @package    core
+ * @copyright  Andrew Lyons <andrew@nicols.co.uk>
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+final class data_provider_finished_subscriber implements DataProviderMethodFinishedSubscriber {
+    /** @var ?int The number of DB writes */
+    private static ?int $dbwrites = null;
+
+    #[\Override]
+    public function notify(DataProviderMethodFinished $event): void {
+        $resetall = false;
+
+        // Note: All of these checks must be extremely lightweight.
+        // This method is called after every single Data Provider.
+        if ($this->is_page_set()) {
+            $this->trigger_notice($event, "has set the theme");
+            $resetall = true;
+        }
+
+        if ($this->is_db_written()) {
+            $this->trigger_notice($event, "has written to the database");
+            $resetall = true;
+        }
+
+        if ($resetall) {
+            \phpunit_util::reset_all_data();
+            $this->update_db_writes();
+        }
+    }
+
+    /**
+     * Check whether the page/theme has been initialised.
+     *
+     * Data Providers should not rely on the page/theme being set.
+     *
+     * @return bool
+     */
+    private function is_page_set(): bool {
+        global $PAGE;
+
+        return (new \ReflectionProperty(\moodle_page::class, '_theme'))->getValue($PAGE) !== null;
+    }
+
+    /**
+     * Check whether the database has been written to.
+     *
+     * Data Providers should not rely on the database being written to.
+     *
+     * @return bool
+     */
+    private function is_db_written(): bool {
+        global $DB;
+
+        if (!$DB) {
+            // DB not initialised yet.
+            return false;
+        }
+
+        if (self::$dbwrites === null) {
+            self::$dbwrites = $DB->perf_get_writes();
+        }
+
+        return $DB->perf_get_writes() > self::$dbwrites;
+    }
+
+    /**
+     * Update the database write count.
+     */
+    private function update_db_writes(): void {
+        global $DB;
+
+        self::$dbwrites = $DB->perf_get_writes();
+    }
+
+    /**
+     * Trigger a warning on the CLI.
+     *
+     * Note: PHPUnit does not let us actually emit a notice or warning for the DataProviderFinished event.
+     *
+     * @param DataProviderMethodFinished $event
+     * @param string $message
+     */
+    private function trigger_notice(DataProviderMethodFinished $event, string $message): void {
+        printf(
+            "Warning: Data provider for %s::%s %s%s",
+            $event->testMethod()->className(),
+            $event->testMethod()->methodName(),
+            $message,
+            PHP_EOL,
+        );
+    }
+}
diff --git a/lib/tests/classes/phpunit/moodle_extension.php b/lib/tests/classes/phpunit/moodle_extension.php
new file mode 100644
index 00000000000..98f8b36ed7b
--- /dev/null
+++ b/lib/tests/classes/phpunit/moodle_extension.php
@@ -0,0 +1,44 @@
+<?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\tests\phpunit;
+
+use PHPUnit\Runner\Extension\Extension;
+use PHPUnit\Runner\Extension\Facade;
+use PHPUnit\Runner\Extension\ParameterCollection;
+use PHPUnit\TextUI\Configuration\Configuration;
+
+/**
+ * Moodle PHPUnit Extension Registration.
+ *
+ * @package    core
+ * @copyright  Andrew Lyons <andrew@nicols.co.uk>
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+final class moodle_extension implements Extension {
+    #[\Override]
+    public function bootstrap(
+        Configuration $configuration,
+        Facade $facade,
+        ParameterCollection $parameters
+    ): void {
+        if ($configuration->noOutput()) {
+            return;
+        }
+
+        $facade->registerSubscriber(new data_provider_finished_subscriber());
+    }
+}
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index 221efb8273a..ba39acf2253 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -30,6 +30,10 @@
         uncomment and alter to fetch external test files from alternative location-->
   </php>
 
+  <extensions>
+    <bootstrap class="core\tests\phpunit\moodle_extension"/>
+  </extensions>
+
   <!--All core suites need to be manually added here-->
 
   <testsuites>