diff --git a/Tests/GeoIP2AdapterTest.php b/Tests/GeoIP2AdapterTest.php
index 19272f0..a15f850 100644
--- a/Tests/GeoIP2AdapterTest.php
+++ b/Tests/GeoIP2AdapterTest.php
@@ -14,6 +14,7 @@
 
 use Geocoder\Provider\GeoIP2\GeoIP2Adapter;
 use RuntimeException;
+use PHPUnit\Framework\MockObject\MockObject;
 use PHPUnit\Framework\TestCase;
 
 /**
@@ -121,7 +122,7 @@ public function testReaderResponseIsJsonEncoded()
     }
 
     /**
-     * @return \PHPUnit_Framework_MockObject_MockObject
+     * @return MockObject
      */
     protected function getGeoIP2ProviderMock()
     {
@@ -131,9 +132,9 @@ protected function getGeoIP2ProviderMock()
     }
 
     /**
-     * @param int $geoIP2Model (e.g. GeoIP2Adapter::GEOIP2_MODEL_CITY, ...)
+     * @param string $geoIP2Model (e.g. GeoIP2Adapter::GEOIP2_MODEL_CITY, ...)
      *
-     * @return \PHPUnit_Framework_MockObject_MockObject
+     * @return MockObject
      */
     protected function getGeoIP2ModelMock($geoIP2Model)
     {
diff --git a/Tests/GeoIP2Test.php b/Tests/GeoIP2Test.php
index decbca2..aee4203 100644
--- a/Tests/GeoIP2Test.php
+++ b/Tests/GeoIP2Test.php
@@ -24,6 +24,7 @@
 use GeoIp2\Exception\OutOfQueriesException;
 use Geocoder\Exception\InvalidCredentials;
 use Geocoder\Exception\QuotaExceeded;
+use PHPUnit\Framework\MockObject\MockObject;
 
 /**
  * @author Jens Wiese <jens@howtrueisfalse.de>
@@ -261,7 +262,7 @@ public static function provideDataForTestingExceptions(): array
     /**
      * @param mixed $returnValue
      *
-     * @return \PHPUnit_Framework_MockObject_MockObject|GeoIP2Adapter
+     * @return GeoIP2Adapter&MockObject
      */
     private function getGeoIP2AdapterMock($returnValue = '')
     {
diff --git a/Tests/IntegrationTest.php b/Tests/IntegrationTest.php
index e0cac86..b3251d3 100644
--- a/Tests/IntegrationTest.php
+++ b/Tests/IntegrationTest.php
@@ -23,13 +23,13 @@
  */
 class IntegrationTest extends ProviderIntegrationTest
 {
-    protected $testAddress = false;
+    protected bool $testAddress = false;
 
-    protected $testReverse = false;
+    protected bool $testReverse = false;
 
-    protected $testIpv6 = false;
+    protected bool $testIpv6 = false;
 
-    protected $testHttpProvider = false;
+    protected bool $testHttpProvider = false;
 
     protected function createProvider(ClientInterface $httpClient)
     {
@@ -38,13 +38,13 @@ protected function createProvider(ClientInterface $httpClient)
         return new GeoIP2(new GeoIP2Adapter($reader));
     }
 
-    protected function getCacheDir()
+    protected function getCacheDir(): string
     {
         return __DIR__.'/.cached_responses';
     }
 
-    protected function getApiKey()
+    protected function getApiKey(): string
     {
-        return null;
+        return '';
     }
 }