diff --git a/.gitignore b/.gitignore
index b693fac..a13ce21 100644
--- a/.gitignore
+++ b/.gitignore
@@ -22,6 +22,7 @@
 /.php-cs-fixer.cache
 
 # PHPUnit
+/.phpunit.cache/
 /.phpunit.result.cache
 
 # WordPress
diff --git a/composer.json b/composer.json
index 75348cb..9440b59 100644
--- a/composer.json
+++ b/composer.json
@@ -39,6 +39,12 @@
 			"automattic/jetpack-autoloader": true
 		}
 	},
+	"repositories": [
+		{
+			"url": "https://github.com/wordpress/sqlite-database-integration.git",
+			"type": "git"
+		}
+	],
 	"require": {
 		"php": ">=8.0",
 		"automattic/jetpack-autoloader": "^3.0",
@@ -56,7 +62,8 @@
 		"roots/wordpress": "^6.4",
 		"sirbrillig/phpcs-variable-analysis": "^2.11",
 		"slevomat/coding-standard": "^8.15",
-		"wp-phpunit/wp-phpunit": "^6.4",
+		"wordpress/sqlite-database-integration": "^2.1",
+		"wp-phpunit/wp-phpunit": "^6.5",
 		"yoast/phpunit-polyfills": "^2.0"
 	},
 	"scripts": {
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index 0554948..0ddf1f8 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -1,22 +1,19 @@
 <?xml version="1.0" encoding="UTF-8"?>
 
-<phpunit
-    bootstrap="tests/bootstrap.php"
-    backupGlobals="false"
-    colors="true"
-    convertErrorsToExceptions="true"
-    convertNoticesToExceptions="true"
-    convertWarningsToExceptions="true"
->
+<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" bootstrap="tests/bootstrap.php" backupGlobals="false" colors="true" xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/10.5/phpunit.xsd" cacheDirectory=".phpunit.cache">
     <testsuites>
         <testsuite name="unit">
             <directory>tests/src</directory>
         </testsuite>
     </testsuites>
-
-    <coverage>
+  
+    <php>
+        <env name="WP_PHPUNIT__TESTS_CONFIG" value="tests/wp-config.php"/>
+    </php>
+  
+    <source>
         <include>
             <directory>src</directory>
         </include>
-    </coverage>
+    </source>
 </phpunit>
diff --git a/tests/bootstrap.php b/tests/bootstrap.php
index 012503c..4c7cbac 100644
--- a/tests/bootstrap.php
+++ b/tests/bootstrap.php
@@ -8,17 +8,67 @@
  * @package   Pronamic\WordPress\Pay\Gateways\OmniKassa2
  */
 
-putenv( 'WP_PHPUNIT__TESTS_CONFIG=tests/wp-config.php' );
+/**
+ * Give access to tests_add_filter() function.
+ * 
+ * @link https://github.com/wp-phpunit/example-plugin/blob/master/tests/bootstrap.php
+ */
+require_once getenv( 'WP_PHPUNIT__DIR' ) . '/includes/functions.php';
 
-require_once __DIR__ . '/../vendor/autoload.php';
+/**
+ * Psalm.
+ */
+if ( defined( 'PSALM_VERSION' ) ) {
+	return;
+}
 
-require_once getenv( 'WP_PHPUNIT__DIR' ) . '/includes/functions.php';
+/**
+ * SQLite integration.
+ * 
+ * @link https://github.com/WordPress/sqlite-database-integration/issues/7#issuecomment-1646660980
+ * @link https://github.com/wp-phpunit/example-plugin/blob/master/tests/bootstrap.php
+ * @link https://github.com/WordPress/wordpress-playground/blob/23c0fc6aae5d090a14d352160c34d39988167406/packages/playground/wordpress/build/Dockerfile#L25-L42
+ */
+if ( ! is_dir( __DIR__ . '/../wordpress/wp-content/' ) ) {
+	// phpcs:ignore WordPressVIPMinimum.Functions.RestrictedFunctions.directory_mkdir
+	mkdir( __DIR__ . '/../wordpress/wp-content/' );
+}
 
+$db_dropin_file = __DIR__ . '/../wordpress/wp-content/db.php';
+
+if ( ! is_file( $db_dropin_file ) ) {
+	// phpcs:ignore WordPressVIPMinimum.Functions.RestrictedFunctions.file_ops_file_put_contents
+	file_put_contents(
+		$db_dropin_file,
+		str_replace(
+			[
+				'{SQLITE_IMPLEMENTATION_FOLDER_PATH}',
+				'{SQLITE_PLUGIN}',
+			],
+			[
+				__DIR__ . '/../vendor/wordpress/sqlite-database-integration',
+				'sqlite-database-integration/load.php',
+			],
+			file_get_contents( __DIR__ . '/../vendor/wordpress/sqlite-database-integration/db.copy' )
+		)
+	);
+}
+
+/**
+ * Plugin.
+ */
 tests_add_filter(
 	'muplugins_loaded',
-	function() {
+	function () {
+		require __DIR__ . '/../vendor/wordpress/sqlite-database-integration/load.php';
+
 		require __DIR__ . '/../pronamic-pay-with-rabo-smart-pay.php';
-	}
+	} 
 );
 
+/**
+ * Start up the WP testing environment.
+ * 
+ * @link https://github.com/wp-phpunit/example-plugin/blob/master/tests/bootstrap.php
+ */
 require getenv( 'WP_PHPUNIT__DIR' ) . '/includes/bootstrap.php';
diff --git a/tests/src/AddressTest.php b/tests/src/AddressTest.php
index 97e9029..be35b8c 100644
--- a/tests/src/AddressTest.php
+++ b/tests/src/AddressTest.php
@@ -10,7 +10,7 @@
 
 namespace Pronamic\WordPress\Pay\Gateways\OmniKassa2;
 
-use PHPUnit\Framework\TestCase;
+use Yoast\PHPUnitPolyfills\TestCases\TestCase;
 
 /**
  * Address test
diff --git a/tests/src/DataHelperTest.php b/tests/src/DataHelperTest.php
index fd7cb79..130c7c0 100644
--- a/tests/src/DataHelperTest.php
+++ b/tests/src/DataHelperTest.php
@@ -10,7 +10,7 @@
 
 namespace Pronamic\WordPress\Pay\Gateways\OmniKassa2;
 
-use PHPUnit\Framework\TestCase;
+use Yoast\PHPUnitPolyfills\TestCases\TestCase;
 
 /**
  * Data helper test
diff --git a/tests/src/ErrorTest.php b/tests/src/ErrorTest.php
index 0d2044a..01d148f 100644
--- a/tests/src/ErrorTest.php
+++ b/tests/src/ErrorTest.php
@@ -10,6 +10,8 @@
 
 namespace Pronamic\WordPress\Pay\Gateways\OmniKassa2;
 
+use Yoast\PHPUnitPolyfills\TestCases\TestCase;
+
 /**
  * Error test
  *
@@ -17,7 +19,7 @@
  * @version 2.1.10
  * @since   2.0.2
  */
-class ErrorTest extends \PHPUnit\Framework\TestCase {
+class ErrorTest extends TestCase {
 	/**
 	 * Get test error.
 	 *
diff --git a/tests/src/NotificationTest.php b/tests/src/NotificationTest.php
index 12233db..8dc641b 100644
--- a/tests/src/NotificationTest.php
+++ b/tests/src/NotificationTest.php
@@ -10,7 +10,7 @@
 
 namespace Pronamic\WordPress\Pay\Gateways\OmniKassa2;
 
-use PHPUnit\Framework\TestCase;
+use Yoast\PHPUnitPolyfills\TestCases\TestCase;
 
 /**
  * Notification test
diff --git a/tests/src/OrderAnnounceResponseTest.php b/tests/src/OrderAnnounceResponseTest.php
index 7a6046a..ebd5e01 100644
--- a/tests/src/OrderAnnounceResponseTest.php
+++ b/tests/src/OrderAnnounceResponseTest.php
@@ -10,7 +10,7 @@
 
 namespace Pronamic\WordPress\Pay\Gateways\OmniKassa2;
 
-use PHPUnit\Framework\TestCase;
+use Yoast\PHPUnitPolyfills\TestCases\TestCase;
 
 /**
  * Order results test
diff --git a/tests/src/OrderItemTest.php b/tests/src/OrderItemTest.php
index 9c5085a..34eca6f 100644
--- a/tests/src/OrderItemTest.php
+++ b/tests/src/OrderItemTest.php
@@ -10,7 +10,7 @@
 
 namespace Pronamic\WordPress\Pay\Gateways\OmniKassa2;
 
-use PHPUnit\Framework\TestCase;
+use Yoast\PHPUnitPolyfills\TestCases\TestCase;
 
 /**
  * Order item test
diff --git a/tests/src/OrderResultsTest.php b/tests/src/OrderResultsTest.php
index 8134b38..097a3e3 100644
--- a/tests/src/OrderResultsTest.php
+++ b/tests/src/OrderResultsTest.php
@@ -10,7 +10,7 @@
 
 namespace Pronamic\WordPress\Pay\Gateways\OmniKassa2;
 
-use PHPUnit\Framework\TestCase;
+use Yoast\PHPUnitPolyfills\TestCases\TestCase;
 
 /**
  * Order results test
diff --git a/tests/src/OrderTest.php b/tests/src/OrderTest.php
index f556000..f5abefd 100644
--- a/tests/src/OrderTest.php
+++ b/tests/src/OrderTest.php
@@ -11,7 +11,7 @@
 namespace Pronamic\WordPress\Pay\Gateways\OmniKassa2;
 
 use DateTime;
-use PHPUnit\Framework\TestCase;
+use Yoast\PHPUnitPolyfills\TestCases\TestCase;
 
 /**
  * Order test
diff --git a/tests/src/PaymentBrandsTest.php b/tests/src/PaymentBrandsTest.php
index 92efafe..93b63fc 100644
--- a/tests/src/PaymentBrandsTest.php
+++ b/tests/src/PaymentBrandsTest.php
@@ -10,8 +10,8 @@
 
 namespace Pronamic\WordPress\Pay\Gateways\OmniKassa2;
 
-use PHPUnit\Framework\TestCase;
 use Pronamic\WordPress\Pay\Core\PaymentMethods;
+use Yoast\PHPUnitPolyfills\TestCases\TestCase;
 
 /**
  * Payment brands test
diff --git a/tests/src/ReturnParametersTest.php b/tests/src/ReturnParametersTest.php
index 51aa523..c056ace 100644
--- a/tests/src/ReturnParametersTest.php
+++ b/tests/src/ReturnParametersTest.php
@@ -10,7 +10,7 @@
 
 namespace Pronamic\WordPress\Pay\Gateways\OmniKassa2;
 
-use PHPUnit\Framework\TestCase;
+use Yoast\PHPUnitPolyfills\TestCases\TestCase;
 
 /**
  * Return parameters test
diff --git a/tests/src/SecurityTest.php b/tests/src/SecurityTest.php
index c6093b0..6acc630 100644
--- a/tests/src/SecurityTest.php
+++ b/tests/src/SecurityTest.php
@@ -10,7 +10,7 @@
 
 namespace Pronamic\WordPress\Pay\Gateways\OmniKassa2;
 
-use PHPUnit\Framework\TestCase;
+use Yoast\PHPUnitPolyfills\TestCases\TestCase;
 
 /**
  * Security test
diff --git a/tests/src/StatusesTest.php b/tests/src/StatusesTest.php
index 243c6f0..a3d3458 100644
--- a/tests/src/StatusesTest.php
+++ b/tests/src/StatusesTest.php
@@ -10,8 +10,8 @@
 
 namespace Pronamic\WordPress\Pay\Gateways\OmniKassa2;
 
-use PHPUnit\Framework\TestCase;
 use Pronamic\WordPress\Pay\Payments\PaymentStatus;
+use Yoast\PHPUnitPolyfills\TestCases\TestCase;
 
 /**
  * Statuses test
diff --git a/tests/src/WebhookControllerTest.php b/tests/src/WebhookControllerTest.php
index ab0863c..aac0f3a 100644
--- a/tests/src/WebhookControllerTest.php
+++ b/tests/src/WebhookControllerTest.php
@@ -15,12 +15,12 @@
 use Pronamic\WordPress\Pay\Payments\PaymentStatus;
 use Pronamic\WordPress\Pay\Plugin;
 use WP_REST_Request;
-use WP_UnitTestCase;
+use Yoast\PHPUnitPolyfills\TestCases\TestCase;
 
 /**
  * Webhook controller test class
  */
-class WebhookControllerTest extends WP_UnitTestCase {
+class WebhookControllerTest extends TestCase {
 	/**
 	 * REST server.
 	 *