diff --git a/includes/auth/AuthManager.php b/includes/auth/AuthManager.php
index 50b531e3535..5ab2b00ba93 100644
--- a/includes/auth/AuthManager.php
+++ b/includes/auth/AuthManager.php
@@ -133,9 +133,6 @@ class AuthManager implements LoggerAwareInterface {
 	/** Auto-creation is due to a Maintenance script */
 	public const AUTOCREATE_SOURCE_MAINT = '::Maintenance::';
 
-	/** @var AuthManager|null */
-	private static $instance = null;
-
 	/** @var WebRequest */
 	private $request;
 
@@ -2472,21 +2469,6 @@ class AuthManager implements LoggerAwareInterface {
 		}
 	}
 
-	/**
-	 * Reset the internal caching for unit testing
-	 * @note Unit tests only
-	 * @internal
-	 */
-	public static function resetCache() {
-		if ( !defined( 'MW_PHPUNIT_TEST' ) ) {
-			// @codeCoverageIgnoreStart
-			throw new \MWException( __METHOD__ . ' may only be called from unit tests!' );
-			// @codeCoverageIgnoreEnd
-		}
-
-		self::$instance = null;
-	}
-
 	/**
 	 * @return HookContainer
 	 */
diff --git a/tests/phpunit/MediaWikiIntegrationTestCase.php b/tests/phpunit/MediaWikiIntegrationTestCase.php
index 180c6d5babd..4572b40e55a 100644
--- a/tests/phpunit/MediaWikiIntegrationTestCase.php
+++ b/tests/phpunit/MediaWikiIntegrationTestCase.php
@@ -645,7 +645,6 @@ abstract class MediaWikiIntegrationTestCase extends PHPUnit\Framework\TestCase {
 		}
 		$wgRequest = RequestContext::getMain()->getRequest();
 		MediaWiki\Session\SessionManager::resetCache();
-		MediaWiki\Auth\AuthManager::resetCache();
 
 		// If anything changed the content language, we need to
 		// reset the SpecialPageFactory.
diff --git a/tests/phpunit/includes/api/ApiTestCase.php b/tests/phpunit/includes/api/ApiTestCase.php
index cad7aae7c28..d90d6f1886c 100644
--- a/tests/phpunit/includes/api/ApiTestCase.php
+++ b/tests/phpunit/includes/api/ApiTestCase.php
@@ -110,7 +110,6 @@ abstract class ApiTestCase extends MediaWikiLangTestCase {
 		$wgRequest = $this->buildFauxRequest( $params, $sessionObj );
 		RequestContext::getMain()->setRequest( $wgRequest );
 		RequestContext::getMain()->setAuthority( $performer );
-		MediaWiki\Auth\AuthManager::resetCache();
 
 		// set up local environment
 		$context = $this->apiContext->newTestContext( $wgRequest, $performer );