diff --git a/Tests/GeoIP2AdapterTest.php b/Tests/GeoIP2AdapterTest.php
index f1ca60a..6ec1548 100644
--- a/Tests/GeoIP2AdapterTest.php
+++ b/Tests/GeoIP2AdapterTest.php
@@ -41,13 +41,13 @@ public function setUp(): void
         $this->adapter = new GeoIP2Adapter($this->getGeoIP2ProviderMock());
     }
 
-    public function testGetName()
+    public function testGetName(): void
     {
         $expectedName = 'maxmind_geoip2';
         $this->assertEquals($expectedName, $this->adapter->getName());
     }
 
-    public function testGetContentMustBeCalledWithUrl()
+    public function testGetContentMustBeCalledWithUrl(): void
     {
         $this->expectException(\Geocoder\Exception\InvalidArgument::class);
         $this->expectExceptionMessage('must be called with a valid url. Got "127.0.0.1" instead.');
@@ -56,7 +56,7 @@ public function testGetContentMustBeCalledWithUrl()
         $this->adapter->getContent($url);
     }
 
-    public function testAddressPassedToReaderMustBeIpAddress()
+    public function testAddressPassedToReaderMustBeIpAddress(): void
     {
         $this->expectException(\Geocoder\Exception\InvalidArgument::class);
         $this->expectExceptionMessage('URL must contain a valid query-string (an IP address, 127.0.0.1 for instance)');
@@ -65,7 +65,10 @@ public function testAddressPassedToReaderMustBeIpAddress()
         $this->adapter->getContent($url);
     }
 
-    public static function provideDataForSwitchingRequestMethods()
+    /**
+     * @return array<string[]>
+     */
+    public static function provideDataForSwitchingRequestMethods(): array
     {
         return [
             [GeoIP2Adapter::GEOIP2_MODEL_CITY],
@@ -76,7 +79,7 @@ public static function provideDataForSwitchingRequestMethods()
     /**
      * @dataProvider provideDataForSwitchingRequestMethods
      */
-    public function testIpAddressIsPassedCorrectToReader($geoIp2Model)
+    public function testIpAddressIsPassedCorrectToReader(string $geoIp2Model): void
     {
         $geoIp2Provider = $this->getGeoIP2ProviderMock();
         $geoIp2Provider
@@ -91,7 +94,7 @@ public function testIpAddressIsPassedCorrectToReader($geoIp2Model)
         $adapter->getContent('file://geoip?127.0.0.1');
     }
 
-    public function testNotSupportedGeoIP2ModelLeadsToException()
+    public function testNotSupportedGeoIP2ModelLeadsToException(): void
     {
         $this->expectException(\Geocoder\Exception\UnsupportedOperation::class);
         $this->expectExceptionMessage('Model "unsupported_model" is not available.');
@@ -99,7 +102,7 @@ public function testNotSupportedGeoIP2ModelLeadsToException()
         new GeoIP2Adapter($this->getGeoIP2ProviderMock(), 'unsupported_model');
     }
 
-    public function testReaderResponseIsJsonEncoded()
+    public function testReaderResponseIsJsonEncoded(): void
     {
         $cityModel = $this->getGeoIP2ModelMock(GeoIP2Adapter::GEOIP2_MODEL_CITY);
 
@@ -135,6 +138,7 @@ protected function getGeoIP2ProviderMock()
      */
     protected function getGeoIP2ModelMock($geoIP2Model)
     {
+        /** @var class-string $mockClass */
         $mockClass = '\\GeoIp2\\Model\\'.ucfirst($geoIP2Model);
 
         $mock = $this->getMockBuilder($mockClass)->disableOriginalConstructor()->getMock();
diff --git a/Tests/GeoIP2Test.php b/Tests/GeoIP2Test.php
index a96796f..3ce72e4 100644
--- a/Tests/GeoIP2Test.php
+++ b/Tests/GeoIP2Test.php
@@ -41,17 +41,17 @@ public function setUp(): void
         $this->provider = new GeoIP2($this->getGeoIP2AdapterMock());
     }
 
-    protected function getCacheDir()
+    protected function getCacheDir(): string
     {
         return __DIR__.'/.cached_responses';
     }
 
-    public function testGetName()
+    public function testGetName(): void
     {
         $this->assertEquals('geoip2', $this->provider->getName());
     }
 
-    public function testQueryingReverseLeadsToException()
+    public function testQueryingReverseLeadsToException(): void
     {
         $this->expectException(\Geocoder\Exception\UnsupportedOperation::class);
         $this->expectExceptionMessage('The GeoIP2 provider is not able to do reverse geocoding.');
@@ -59,7 +59,7 @@ public function testQueryingReverseLeadsToException()
         $this->provider->reverseQuery(ReverseQuery::fromCoordinates(50, 9));
     }
 
-    public function testGeocodeWithLocalhostIPv4()
+    public function testGeocodeWithLocalhostIPv4(): void
     {
         $results = $this->provider->geocodeQuery(GeocodeQuery::create('127.0.0.1'));
 
@@ -73,7 +73,7 @@ public function testGeocodeWithLocalhostIPv4()
         $this->assertEquals('localhost', $result->getCountry()->getName());
     }
 
-    public function testOnlyIpAddressesCouldBeResolved()
+    public function testOnlyIpAddressesCouldBeResolved(): void
     {
         $this->expectException(\Geocoder\Exception\UnsupportedOperation::class);
         $this->expectExceptionMessage('The GeoIP2 provider does not support street addresses, only IP addresses.');
@@ -84,7 +84,7 @@ public function testOnlyIpAddressesCouldBeResolved()
     /**
      * Provides data for geocode test.
      *
-     * @return array
+     * @return array<string, array<array<string, array<array<string, string>>|float|int|string|null>|string>>
      */
     public static function provideDataForRetrievingGeodata()
     {
@@ -163,9 +163,9 @@ public static function provideDataForRetrievingGeodata()
     /**
      * @dataProvider provideDataForRetrievingGeodata
      *
-     * @param string $address
+     * @param array<string, mixed> $expectedGeodata
      */
-    public function testRetrievingGeodata($address, $adapterResponse, $expectedGeodata)
+    public function testRetrievingGeodata(string $address, string $adapterResponse, array $expectedGeodata): void
     {
         $adapter = $this->getGeoIP2AdapterMock($adapterResponse);
         $provider = new GeoIP2($adapter);
@@ -212,7 +212,7 @@ public function testRetrievingGeodata($address, $adapterResponse, $expectedGeoda
         }
     }
 
-    public function testRetrievingGeodataNotExistingLocation()
+    public function testRetrievingGeodataNotExistingLocation(): void
     {
         $adapter = $this->getGeoIP2AdapterMock('');
         $provider = new GeoIP2($adapter);
@@ -222,7 +222,7 @@ public function testRetrievingGeodataNotExistingLocation()
         $this->assertEquals(0, $result->count());
     }
 
-    public function testGeoIp2Encoding()
+    public function testGeoIp2Encoding(): void
     {
         $reader = new Reader(__DIR__.'/fixtures/GeoLite2-City.mmdb');
         $adapter = new GeoIP2Adapter($reader);
@@ -234,7 +234,7 @@ public function testGeoIp2Encoding()
     /**
      * @dataProvider provideDataForTestingExceptions
      */
-    public function testExceptionConversion(\Exception $original, string $replacementClass)
+    public function testExceptionConversion(\Exception $original, string $replacementClass): void
     {
         $adapter = $this->getGeoIP2AdapterMock($original);
         $provider = new GeoIP2($adapter);
@@ -246,6 +246,9 @@ public function testExceptionConversion(\Exception $original, string $replacemen
         $results = $provider->geocodeQuery(GeocodeQuery::create('74.200.247.59'));
     }
 
+    /**
+     * @return array<array<AuthenticationException|OutOfQueriesException|class-string>>
+     */
     public static function provideDataForTestingExceptions(): array
     {
         return [
@@ -255,6 +258,8 @@ public static function provideDataForTestingExceptions(): array
     }
 
     /**
+     * @param \Exception|string $returnValue
+     *
      * @return GeoIP2Adapter&MockObject
      */
     private function getGeoIP2AdapterMock($returnValue = '')