diff --git a/module/CLI/test/Command/Api/DisableKeyCommandTest.php b/module/CLI/test/Command/Api/DisableKeyCommandTest.php
index 552e1060..c0a36f1d 100644
--- a/module/CLI/test/Command/Api/DisableKeyCommandTest.php
+++ b/module/CLI/test/Command/Api/DisableKeyCommandTest.php
@@ -14,9 +14,9 @@ use Symfony\Component\Console\Tester\CommandTester;
 class DisableKeyCommandTest extends TestCase
 {
     /** @var CommandTester */
-    protected $commandTester;
+    private $commandTester;
     /** @var ObjectProphecy */
-    protected $apiKeyService;
+    private $apiKeyService;
 
     public function setUp()
     {
diff --git a/module/CLI/test/Command/Api/GenerateKeyCommandTest.php b/module/CLI/test/Command/Api/GenerateKeyCommandTest.php
index 73e4b4ae..104af2b3 100644
--- a/module/CLI/test/Command/Api/GenerateKeyCommandTest.php
+++ b/module/CLI/test/Command/Api/GenerateKeyCommandTest.php
@@ -16,9 +16,9 @@ use Symfony\Component\Console\Tester\CommandTester;
 class GenerateKeyCommandTest extends TestCase
 {
     /** @var CommandTester */
-    protected $commandTester;
+    private $commandTester;
     /** @var ObjectProphecy */
-    protected $apiKeyService;
+    private $apiKeyService;
 
     public function setUp()
     {
diff --git a/module/CLI/test/Command/Api/ListKeysCommandTest.php b/module/CLI/test/Command/Api/ListKeysCommandTest.php
index b71b3a0a..5a656073 100644
--- a/module/CLI/test/Command/Api/ListKeysCommandTest.php
+++ b/module/CLI/test/Command/Api/ListKeysCommandTest.php
@@ -14,9 +14,9 @@ use Symfony\Component\Console\Tester\CommandTester;
 class ListKeysCommandTest extends TestCase
 {
     /** @var CommandTester */
-    protected $commandTester;
+    private $commandTester;
     /** @var ObjectProphecy */
-    protected $apiKeyService;
+    private $apiKeyService;
 
     public function setUp()
     {
diff --git a/module/CLI/test/Command/Config/GenerateCharsetCommandTest.php b/module/CLI/test/Command/Config/GenerateCharsetCommandTest.php
index 70ea2a71..33e0d173 100644
--- a/module/CLI/test/Command/Config/GenerateCharsetCommandTest.php
+++ b/module/CLI/test/Command/Config/GenerateCharsetCommandTest.php
@@ -14,7 +14,7 @@ use function str_split;
 class GenerateCharsetCommandTest extends TestCase
 {
     /** @var CommandTester */
-    protected $commandTester;
+    private $commandTester;
 
     public function setUp()
     {
diff --git a/module/CLI/test/Command/ShortUrl/GeneratePreviewCommandTest.php b/module/CLI/test/Command/ShortUrl/GeneratePreviewCommandTest.php
index 2a1dda39..a9fa2844 100644
--- a/module/CLI/test/Command/ShortUrl/GeneratePreviewCommandTest.php
+++ b/module/CLI/test/Command/ShortUrl/GeneratePreviewCommandTest.php
@@ -21,7 +21,7 @@ use function substr_count;
 class GeneratePreviewCommandTest extends TestCase
 {
     /** @var CommandTester */
-    protected $commandTester;
+    private $commandTester;
     /** @var ObjectProphecy */
     private $previewGenerator;
     /** @var ObjectProphecy */
diff --git a/module/CLI/test/Command/ShortUrl/GenerateShortUrlCommandTest.php b/module/CLI/test/Command/ShortUrl/GenerateShortUrlCommandTest.php
index 9056aed7..4698ed48 100644
--- a/module/CLI/test/Command/ShortUrl/GenerateShortUrlCommandTest.php
+++ b/module/CLI/test/Command/ShortUrl/GenerateShortUrlCommandTest.php
@@ -18,9 +18,9 @@ use Symfony\Component\Console\Tester\CommandTester;
 class GenerateShortUrlCommandTest extends TestCase
 {
     /** @var CommandTester */
-    protected $commandTester;
+    private $commandTester;
     /** @var ObjectProphecy */
-    protected $urlShortener;
+    private $urlShortener;
 
     public function setUp()
     {
diff --git a/module/CLI/test/Command/ShortUrl/GetVisitsCommandTest.php b/module/CLI/test/Command/ShortUrl/GetVisitsCommandTest.php
index bbca65ec..9c4947dd 100644
--- a/module/CLI/test/Command/ShortUrl/GetVisitsCommandTest.php
+++ b/module/CLI/test/Command/ShortUrl/GetVisitsCommandTest.php
@@ -21,9 +21,9 @@ use function strpos;
 class GetVisitsCommandTest extends TestCase
 {
     /** @var CommandTester */
-    protected $commandTester;
+    private $commandTester;
     /** @var ObjectProphecy */
-    protected $visitsTracker;
+    private $visitsTracker;
 
     public function setUp()
     {
diff --git a/module/CLI/test/Command/ShortUrl/ListShortUrlsCommandTest.php b/module/CLI/test/Command/ShortUrl/ListShortUrlsCommandTest.php
index c6800cc3..d21b4625 100644
--- a/module/CLI/test/Command/ShortUrl/ListShortUrlsCommandTest.php
+++ b/module/CLI/test/Command/ShortUrl/ListShortUrlsCommandTest.php
@@ -17,9 +17,9 @@ use Zend\Paginator\Paginator;
 class ListShortUrlsCommandTest extends TestCase
 {
     /** @var CommandTester */
-    protected $commandTester;
+    private $commandTester;
     /** @var ObjectProphecy */
-    protected $shortUrlService;
+    private $shortUrlService;
 
     public function setUp()
     {
diff --git a/module/CLI/test/Command/ShortUrl/ResolveUrlCommandTest.php b/module/CLI/test/Command/ShortUrl/ResolveUrlCommandTest.php
index 2cf9df88..46ce05c6 100644
--- a/module/CLI/test/Command/ShortUrl/ResolveUrlCommandTest.php
+++ b/module/CLI/test/Command/ShortUrl/ResolveUrlCommandTest.php
@@ -17,9 +17,9 @@ use const PHP_EOL;
 class ResolveUrlCommandTest extends TestCase
 {
     /** @var CommandTester */
-    protected $commandTester;
+    private $commandTester;
     /** @var ObjectProphecy */
-    protected $urlShortener;
+    private $urlShortener;
 
     public function setUp()
     {
diff --git a/module/CLI/test/ConfigProviderTest.php b/module/CLI/test/ConfigProviderTest.php
index c222e8aa..1f9c33a5 100644
--- a/module/CLI/test/ConfigProviderTest.php
+++ b/module/CLI/test/ConfigProviderTest.php
@@ -9,7 +9,7 @@ use Shlinkio\Shlink\CLI\ConfigProvider;
 class ConfigProviderTest extends TestCase
 {
     /** @var ConfigProvider */
-    protected $configProvider;
+    private $configProvider;
 
     public function setUp()
     {
diff --git a/module/CLI/test/Factory/ApplicationFactoryTest.php b/module/CLI/test/Factory/ApplicationFactoryTest.php
index f7d4db21..00f05cfe 100644
--- a/module/CLI/test/Factory/ApplicationFactoryTest.php
+++ b/module/CLI/test/Factory/ApplicationFactoryTest.php
@@ -16,7 +16,7 @@ use function array_merge;
 class ApplicationFactoryTest extends TestCase
 {
     /** @var ApplicationFactory */
-    protected $factory;
+    private $factory;
 
     public function setUp()
     {
diff --git a/module/Common/test/ConfigProviderTest.php b/module/Common/test/ConfigProviderTest.php
index 3e90fef2..a133ba61 100644
--- a/module/Common/test/ConfigProviderTest.php
+++ b/module/Common/test/ConfigProviderTest.php
@@ -9,7 +9,7 @@ use Shlinkio\Shlink\Common\ConfigProvider;
 class ConfigProviderTest extends TestCase
 {
     /** @var ConfigProvider */
-    protected $configProvider;
+    private $configProvider;
 
     public function setUp()
     {
diff --git a/module/Common/test/Factory/CacheFactoryTest.php b/module/Common/test/Factory/CacheFactoryTest.php
index 13575bb7..24414903 100644
--- a/module/Common/test/Factory/CacheFactoryTest.php
+++ b/module/Common/test/Factory/CacheFactoryTest.php
@@ -20,7 +20,7 @@ use function sys_get_temp_dir;
 class CacheFactoryTest extends TestCase
 {
     /** @var CacheFactory */
-    protected $factory;
+    private $factory;
 
     public function setUp()
     {
diff --git a/module/Common/test/Factory/EmptyResponseImplicitOptionsMiddlewareFactoryTest.php b/module/Common/test/Factory/EmptyResponseImplicitOptionsMiddlewareFactoryTest.php
index f687df16..a254e9f2 100644
--- a/module/Common/test/Factory/EmptyResponseImplicitOptionsMiddlewareFactoryTest.php
+++ b/module/Common/test/Factory/EmptyResponseImplicitOptionsMiddlewareFactoryTest.php
@@ -13,7 +13,7 @@ use Zend\ServiceManager\ServiceManager;
 class EmptyResponseImplicitOptionsMiddlewareFactoryTest extends TestCase
 {
     /** @var EmptyResponseImplicitOptionsMiddlewareFactory */
-    protected $factory;
+    private $factory;
 
     public function setUp()
     {
diff --git a/module/Common/test/Factory/EntityManagerFactoryTest.php b/module/Common/test/Factory/EntityManagerFactoryTest.php
index 2647aad9..c8f5ee0a 100644
--- a/module/Common/test/Factory/EntityManagerFactoryTest.php
+++ b/module/Common/test/Factory/EntityManagerFactoryTest.php
@@ -11,7 +11,7 @@ use Zend\ServiceManager\ServiceManager;
 class EntityManagerFactoryTest extends TestCase
 {
     /** @var EntityManagerFactory */
-    protected $factory;
+    private $factory;
 
     public function setUp()
     {
diff --git a/module/Common/test/Factory/LoggerFactoryTest.php b/module/Common/test/Factory/LoggerFactoryTest.php
index f57c1078..5faf7503 100644
--- a/module/Common/test/Factory/LoggerFactoryTest.php
+++ b/module/Common/test/Factory/LoggerFactoryTest.php
@@ -12,7 +12,7 @@ use Zend\ServiceManager\ServiceManager;
 class LoggerFactoryTest extends TestCase
 {
     /** @var LoggerFactory */
-    protected $factory;
+    private $factory;
 
     public function setUp()
     {
diff --git a/module/Common/test/Factory/TranslatorFactoryTest.php b/module/Common/test/Factory/TranslatorFactoryTest.php
index 0dd5cc01..858635a4 100644
--- a/module/Common/test/Factory/TranslatorFactoryTest.php
+++ b/module/Common/test/Factory/TranslatorFactoryTest.php
@@ -11,7 +11,7 @@ use Zend\ServiceManager\ServiceManager;
 class TranslatorFactoryTest extends TestCase
 {
     /** @var TranslatorFactory */
-    protected $factory;
+    private $factory;
 
     public function setUp()
     {
diff --git a/module/Common/test/Image/ImageBuilderFactoryTest.php b/module/Common/test/Image/ImageBuilderFactoryTest.php
index 1b7488cd..26c38a3a 100644
--- a/module/Common/test/Image/ImageBuilderFactoryTest.php
+++ b/module/Common/test/Image/ImageBuilderFactoryTest.php
@@ -11,7 +11,7 @@ use Zend\ServiceManager\ServiceManager;
 class ImageBuilderFactoryTest extends TestCase
 {
     /** @var ImageBuilderFactory */
-    protected $factory;
+    private $factory;
 
     public function setUp()
     {
diff --git a/module/Common/test/Image/ImageFactoryTest.php b/module/Common/test/Image/ImageFactoryTest.php
index 605b2a01..ad2de87c 100644
--- a/module/Common/test/Image/ImageFactoryTest.php
+++ b/module/Common/test/Image/ImageFactoryTest.php
@@ -12,7 +12,7 @@ use Zend\ServiceManager\ServiceManager;
 class ImageFactoryTest extends TestCase
 {
     /** @var ImageFactory */
-    protected $factory;
+    private $factory;
 
     public function setUp()
     {
diff --git a/module/Common/test/IpGeolocation/IpApiLocationResolverTest.php b/module/Common/test/IpGeolocation/IpApiLocationResolverTest.php
index 0e00a07f..55a1cb07 100644
--- a/module/Common/test/IpGeolocation/IpApiLocationResolverTest.php
+++ b/module/Common/test/IpGeolocation/IpApiLocationResolverTest.php
@@ -14,9 +14,9 @@ use function json_encode;
 class IpApiLocationResolverTest extends TestCase
 {
     /** @var IpApiLocationResolver */
-    protected $ipResolver;
+    private $ipResolver;
     /** @var ObjectProphecy */
-    protected $client;
+    private $client;
 
     public function setUp()
     {
diff --git a/module/Common/test/Middleware/LocaleMiddlewareTest.php b/module/Common/test/Middleware/LocaleMiddlewareTest.php
index 5d34da2e..535e767e 100644
--- a/module/Common/test/Middleware/LocaleMiddlewareTest.php
+++ b/module/Common/test/Middleware/LocaleMiddlewareTest.php
@@ -12,9 +12,9 @@ use Zend\I18n\Translator\Translator;
 class LocaleMiddlewareTest extends TestCase
 {
     /** @var LocaleMiddleware */
-    protected $middleware;
+    private $middleware;
     /** @var Translator */
-    protected $translator;
+    private $translator;
 
     public function setUp()
     {
diff --git a/module/Common/test/Paginator/PaginableRepositoryAdapterTest.php b/module/Common/test/Paginator/PaginableRepositoryAdapterTest.php
index da670c9d..7b0de03b 100644
--- a/module/Common/test/Paginator/PaginableRepositoryAdapterTest.php
+++ b/module/Common/test/Paginator/PaginableRepositoryAdapterTest.php
@@ -11,9 +11,9 @@ use Shlinkio\Shlink\Common\Repository\PaginableRepositoryInterface;
 class PaginableRepositoryAdapterTest extends TestCase
 {
     /** @var PaginableRepositoryAdapter */
-    protected $adapter;
+    private $adapter;
     /** @var ObjectProphecy */
-    protected $repo;
+    private $repo;
 
     public function setUp()
     {
diff --git a/module/Common/test/Service/PreviewGeneratorTest.php b/module/Common/test/Service/PreviewGeneratorTest.php
index 31cad6f7..8e3a779c 100644
--- a/module/Common/test/Service/PreviewGeneratorTest.php
+++ b/module/Common/test/Service/PreviewGeneratorTest.php
@@ -17,11 +17,11 @@ use function urlencode;
 class PreviewGeneratorTest extends TestCase
 {
     /** @var PreviewGenerator */
-    protected $generator;
+    private $generator;
     /** @var ObjectProphecy */
-    protected $image;
+    private $image;
     /** @var ObjectProphecy */
-    protected $filesystem;
+    private $filesystem;
 
     public function setUp()
     {
diff --git a/module/Common/test/Template/Extension/TranslatorExtensionTest.php b/module/Common/test/Template/Extension/TranslatorExtensionTest.php
index 28fc2858..ab97b953 100644
--- a/module/Common/test/Template/Extension/TranslatorExtensionTest.php
+++ b/module/Common/test/Template/Extension/TranslatorExtensionTest.php
@@ -12,7 +12,7 @@ use Zend\I18n\Translator\Translator;
 class TranslatorExtensionTest extends TestCase
 {
     /** @var TranslatorExtension */
-    protected $extension;
+    private $extension;
 
     public function setUp()
     {
diff --git a/module/Core/src/Options/AppOptions.php b/module/Core/src/Options/AppOptions.php
index af18c091..b448b8c0 100644
--- a/module/Core/src/Options/AppOptions.php
+++ b/module/Core/src/Options/AppOptions.php
@@ -12,13 +12,13 @@ class AppOptions extends AbstractOptions
     use StringUtilsTrait;
 
     /** @var string */
-    protected $name = '';
+    private $name = '';
     /** @var string */
-    protected $version = '1.0';
+    private $version = '1.0';
     /** @var string */
-    protected $secretKey = '';
+    private $secretKey = '';
     /** @var string|null */
-    protected $disableTrackParam;
+    private $disableTrackParam;
 
     /**
      * AppOptions constructor.
diff --git a/module/Core/test/Action/PixelActionTest.php b/module/Core/test/Action/PixelActionTest.php
index 164f4a85..65d5ce9d 100644
--- a/module/Core/test/Action/PixelActionTest.php
+++ b/module/Core/test/Action/PixelActionTest.php
@@ -19,11 +19,11 @@ use Zend\Diactoros\ServerRequestFactory;
 class PixelActionTest extends TestCase
 {
     /** @var RedirectAction */
-    protected $action;
+    private $action;
     /** @var ObjectProphecy */
-    protected $urlShortener;
+    private $urlShortener;
     /** @var ObjectProphecy */
-    protected $visitTracker;
+    private $visitTracker;
 
     public function setUp()
     {
diff --git a/module/Core/test/Action/PreviewActionTest.php b/module/Core/test/Action/PreviewActionTest.php
index c210cbec..7517f177 100644
--- a/module/Core/test/Action/PreviewActionTest.php
+++ b/module/Core/test/Action/PreviewActionTest.php
@@ -24,7 +24,7 @@ use function filesize;
 class PreviewActionTest extends TestCase
 {
     /** @var PreviewAction */
-    protected $action;
+    private $action;
     /** @var ObjectProphecy */
     private $previewGenerator;
     /** @var ObjectProphecy */
diff --git a/module/Core/test/Action/QrCodeActionTest.php b/module/Core/test/Action/QrCodeActionTest.php
index 48cbb19e..68e2507d 100644
--- a/module/Core/test/Action/QrCodeActionTest.php
+++ b/module/Core/test/Action/QrCodeActionTest.php
@@ -21,9 +21,9 @@ use Zend\Expressive\Router\RouterInterface;
 class QrCodeActionTest extends TestCase
 {
     /** @var QrCodeAction */
-    protected $action;
+    private $action;
     /** @var ObjectProphecy */
-    protected $urlShortener;
+    private $urlShortener;
 
     public function setUp()
     {
diff --git a/module/Core/test/ConfigProviderTest.php b/module/Core/test/ConfigProviderTest.php
index 83744bc4..1c21f2cb 100644
--- a/module/Core/test/ConfigProviderTest.php
+++ b/module/Core/test/ConfigProviderTest.php
@@ -9,7 +9,7 @@ use Shlinkio\Shlink\Core\ConfigProvider;
 class ConfigProviderTest extends TestCase
 {
     /** @var ConfigProvider */
-    protected $configProvider;
+    private $configProvider;
 
     public function setUp()
     {
diff --git a/module/Core/test/Middleware/QrCodeCacheMiddlewareTest.php b/module/Core/test/Middleware/QrCodeCacheMiddlewareTest.php
index 9820a0db..c67ff13d 100644
--- a/module/Core/test/Middleware/QrCodeCacheMiddlewareTest.php
+++ b/module/Core/test/Middleware/QrCodeCacheMiddlewareTest.php
@@ -16,9 +16,9 @@ use Zend\Diactoros\Uri;
 class QrCodeCacheMiddlewareTest extends TestCase
 {
     /** @var QrCodeCacheMiddleware */
-    protected $middleware;
+    private $middleware;
     /** @var Cache */
-    protected $cache;
+    private $cache;
 
     public function setUp()
     {
diff --git a/module/Core/test/Service/ShortUrlServiceTest.php b/module/Core/test/Service/ShortUrlServiceTest.php
index 82e57da5..1c21afae 100644
--- a/module/Core/test/Service/ShortUrlServiceTest.php
+++ b/module/Core/test/Service/ShortUrlServiceTest.php
@@ -20,9 +20,9 @@ use function count;
 class ShortUrlServiceTest extends TestCase
 {
     /** @var ShortUrlService */
-    protected $service;
+    private $service;
     /** @var ObjectProphecy|EntityManagerInterface */
-    protected $em;
+    private $em;
 
     public function setUp()
     {
diff --git a/module/Core/test/Service/UrlShortenerTest.php b/module/Core/test/Service/UrlShortenerTest.php
index bae4db91..a820e905 100644
--- a/module/Core/test/Service/UrlShortenerTest.php
+++ b/module/Core/test/Service/UrlShortenerTest.php
@@ -24,13 +24,13 @@ use Zend\Diactoros\Uri;
 class UrlShortenerTest extends TestCase
 {
     /** @var UrlShortener */
-    protected $urlShortener;
+    private $urlShortener;
     /** @var ObjectProphecy */
-    protected $em;
+    private $em;
     /** @var ObjectProphecy */
-    protected $httpClient;
+    private $httpClient;
     /** @var ObjectProphecy */
-    protected $slugger;
+    private $slugger;
 
     public function setUp()
     {
diff --git a/module/Core/test/Service/VisitServiceTest.php b/module/Core/test/Service/VisitServiceTest.php
index eb6299a7..49e3b1e9 100644
--- a/module/Core/test/Service/VisitServiceTest.php
+++ b/module/Core/test/Service/VisitServiceTest.php
@@ -21,9 +21,9 @@ use function func_get_args;
 class VisitServiceTest extends TestCase
 {
     /** @var VisitService */
-    protected $visitService;
+    private $visitService;
     /** @var ObjectProphecy */
-    protected $em;
+    private $em;
 
     public function setUp()
     {
diff --git a/module/Core/test/Service/VisitsTrackerTest.php b/module/Core/test/Service/VisitsTrackerTest.php
index 0cfc78b3..11d71968 100644
--- a/module/Core/test/Service/VisitsTrackerTest.php
+++ b/module/Core/test/Service/VisitsTrackerTest.php
@@ -17,9 +17,9 @@ use Shlinkio\Shlink\Core\Service\VisitsTracker;
 class VisitsTrackerTest extends TestCase
 {
     /** @var VisitsTracker */
-    protected $visitsTracker;
+    private $visitsTracker;
     /** @var ObjectProphecy */
-    protected $em;
+    private $em;
 
     public function setUp()
     {
diff --git a/module/Installer/test/Command/InstallCommandTest.php b/module/Installer/test/Command/InstallCommandTest.php
index 82965576..b7aaad49 100644
--- a/module/Installer/test/Command/InstallCommandTest.php
+++ b/module/Installer/test/Command/InstallCommandTest.php
@@ -23,13 +23,13 @@ use Zend\Config\Writer\WriterInterface;
 class InstallCommandTest extends TestCase
 {
     /** @var InstallCommand */
-    protected $command;
+    private $command;
     /** @var CommandTester */
-    protected $commandTester;
+    private $commandTester;
     /** @var ObjectProphecy */
-    protected $configWriter;
+    private $configWriter;
     /** @var ObjectProphecy */
-    protected $filesystem;
+    private $filesystem;
 
     public function setUp()
     {
diff --git a/module/Installer/test/Config/Plugin/LanguageConfigCustomizerTest.php b/module/Installer/test/Config/Plugin/LanguageConfigCustomizerTest.php
index e85f4a04..e9035d1c 100644
--- a/module/Installer/test/Config/Plugin/LanguageConfigCustomizerTest.php
+++ b/module/Installer/test/Config/Plugin/LanguageConfigCustomizerTest.php
@@ -13,9 +13,9 @@ use Symfony\Component\Console\Style\SymfonyStyle;
 class LanguageConfigCustomizerTest extends TestCase
 {
     /** @var LanguageConfigCustomizer */
-    protected $plugin;
+    private $plugin;
     /** @var ObjectProphecy */
-    protected $io;
+    private $io;
 
     public function setUp()
     {
diff --git a/module/Installer/test/ConfigProviderTest.php b/module/Installer/test/ConfigProviderTest.php
index 5c6c1129..db5999b2 100644
--- a/module/Installer/test/ConfigProviderTest.php
+++ b/module/Installer/test/ConfigProviderTest.php
@@ -9,7 +9,7 @@ use Shlinkio\Shlink\Installer\ConfigProvider;
 class ConfigProviderTest extends TestCase
 {
     /** @var ConfigProvider */
-    protected $configProvider;
+    private $configProvider;
 
     public function setUp()
     {
diff --git a/module/Rest/test/Action/AuthenticateActionTest.php b/module/Rest/test/Action/AuthenticateActionTest.php
index 38fc3cda..e90690e6 100644
--- a/module/Rest/test/Action/AuthenticateActionTest.php
+++ b/module/Rest/test/Action/AuthenticateActionTest.php
@@ -16,11 +16,11 @@ use function strpos;
 class AuthenticateActionTest extends TestCase
 {
     /** @var AuthenticateAction */
-    protected $action;
+    private $action;
     /** @var ObjectProphecy */
-    protected $apiKeyService;
+    private $apiKeyService;
     /** @var ObjectProphecy */
-    protected $jwtService;
+    private $jwtService;
 
     public function setUp()
     {
diff --git a/module/Rest/test/Action/ShortUrl/CreateShortUrlActionTest.php b/module/Rest/test/Action/ShortUrl/CreateShortUrlActionTest.php
index 252a0300..db834b3b 100644
--- a/module/Rest/test/Action/ShortUrl/CreateShortUrlActionTest.php
+++ b/module/Rest/test/Action/ShortUrl/CreateShortUrlActionTest.php
@@ -20,9 +20,9 @@ use function strpos;
 class CreateShortUrlActionTest extends TestCase
 {
     /** @var CreateShortUrlAction */
-    protected $action;
+    private $action;
     /** @var ObjectProphecy */
-    protected $urlShortener;
+    private $urlShortener;
 
     public function setUp()
     {
diff --git a/module/Rest/test/Action/ShortUrl/EditShortUrlTagsActionTest.php b/module/Rest/test/Action/ShortUrl/EditShortUrlTagsActionTest.php
index f2976e70..24a26a7a 100644
--- a/module/Rest/test/Action/ShortUrl/EditShortUrlTagsActionTest.php
+++ b/module/Rest/test/Action/ShortUrl/EditShortUrlTagsActionTest.php
@@ -14,7 +14,7 @@ use Zend\Diactoros\ServerRequestFactory;
 class EditShortUrlTagsActionTest extends TestCase
 {
     /** @var EditShortUrlTagsAction */
-    protected $action;
+    private $action;
     /** @var ObjectProphecy */
     private $shortUrlService;
 
diff --git a/module/Rest/test/Action/ShortUrl/ListShortUrlsActionTest.php b/module/Rest/test/Action/ShortUrl/ListShortUrlsActionTest.php
index ebd921ba..a4baaf13 100644
--- a/module/Rest/test/Action/ShortUrl/ListShortUrlsActionTest.php
+++ b/module/Rest/test/Action/ShortUrl/ListShortUrlsActionTest.php
@@ -15,9 +15,9 @@ use Zend\Paginator\Paginator;
 class ListShortUrlsActionTest extends TestCase
 {
     /** @var ListShortUrlsAction */
-    protected $action;
+    private $action;
     /** @var ObjectProphecy */
-    protected $service;
+    private $service;
 
     public function setUp()
     {
diff --git a/module/Rest/test/Action/ShortUrl/ResolveShortUrlActionTest.php b/module/Rest/test/Action/ShortUrl/ResolveShortUrlActionTest.php
index 32419d04..7acd606c 100644
--- a/module/Rest/test/Action/ShortUrl/ResolveShortUrlActionTest.php
+++ b/module/Rest/test/Action/ShortUrl/ResolveShortUrlActionTest.php
@@ -18,9 +18,9 @@ use function strpos;
 class ResolveShortUrlActionTest extends TestCase
 {
     /** @var ResolveShortUrlAction */
-    protected $action;
+    private $action;
     /** @var ObjectProphecy */
-    protected $urlShortener;
+    private $urlShortener;
 
     public function setUp()
     {
diff --git a/module/Rest/test/Action/Visit/GetVisitsActionTest.php b/module/Rest/test/Action/Visit/GetVisitsActionTest.php
index 859c9657..f9dd2e54 100644
--- a/module/Rest/test/Action/Visit/GetVisitsActionTest.php
+++ b/module/Rest/test/Action/Visit/GetVisitsActionTest.php
@@ -17,9 +17,9 @@ use Zend\Diactoros\ServerRequestFactory;
 class GetVisitsActionTest extends TestCase
 {
     /** @var GetVisitsAction */
-    protected $action;
+    private $action;
     /** @var ObjectProphecy */
-    protected $visitsTracker;
+    private $visitsTracker;
 
     public function setUp()
     {
diff --git a/module/Rest/test/Authentication/JWTServiceTest.php b/module/Rest/test/Authentication/JWTServiceTest.php
index 5ff66268..962c1665 100644
--- a/module/Rest/test/Authentication/JWTServiceTest.php
+++ b/module/Rest/test/Authentication/JWTServiceTest.php
@@ -13,7 +13,7 @@ use function time;
 class JWTServiceTest extends TestCase
 {
     /** @var JWTService */
-    protected $service;
+    private $service;
 
     public function setUp()
     {
diff --git a/module/Rest/test/Authentication/Plugin/AuthorizationHeaderPluginTest.php b/module/Rest/test/Authentication/Plugin/AuthorizationHeaderPluginTest.php
index bc7bf86c..80b0dc93 100644
--- a/module/Rest/test/Authentication/Plugin/AuthorizationHeaderPluginTest.php
+++ b/module/Rest/test/Authentication/Plugin/AuthorizationHeaderPluginTest.php
@@ -17,7 +17,7 @@ class AuthorizationHeaderPluginTest extends TestCase
     /** @var AuthorizationHeaderPlugin */
     private $plugin;
     /** @var ObjectProphecy */
-    protected $jwtService;
+    private $jwtService;
 
     public function setUp()
     {
diff --git a/module/Rest/test/ConfigProviderTest.php b/module/Rest/test/ConfigProviderTest.php
index 1b4cbdd3..f9fd0b3f 100644
--- a/module/Rest/test/ConfigProviderTest.php
+++ b/module/Rest/test/ConfigProviderTest.php
@@ -9,7 +9,7 @@ use Shlinkio\Shlink\Rest\ConfigProvider;
 class ConfigProviderTest extends TestCase
 {
     /** @var ConfigProvider */
-    protected $configProvider;
+    private $configProvider;
 
     public function setUp()
     {
diff --git a/module/Rest/test/ErrorHandler/JsonErrorResponseGeneratorTest.php b/module/Rest/test/ErrorHandler/JsonErrorResponseGeneratorTest.php
index 346d2822..e7895ae5 100644
--- a/module/Rest/test/ErrorHandler/JsonErrorResponseGeneratorTest.php
+++ b/module/Rest/test/ErrorHandler/JsonErrorResponseGeneratorTest.php
@@ -11,7 +11,7 @@ use Zend\Diactoros\ServerRequestFactory;
 class JsonErrorResponseGeneratorTest extends TestCase
 {
     /** @var JsonErrorResponseGenerator */
-    protected $errorHandler;
+    private $errorHandler;
 
     public function setUp()
     {
diff --git a/module/Rest/test/Middleware/AuthenticationMiddlewareTest.php b/module/Rest/test/Middleware/AuthenticationMiddlewareTest.php
index 8ff36454..2d1c6075 100644
--- a/module/Rest/test/Middleware/AuthenticationMiddlewareTest.php
+++ b/module/Rest/test/Middleware/AuthenticationMiddlewareTest.php
@@ -32,12 +32,12 @@ use function Zend\Stratigility\middleware;
 class AuthenticationMiddlewareTest extends TestCase
 {
     /** @var AuthenticationMiddleware */
-    protected $middleware;
+    private $middleware;
     /** @var ObjectProphecy */
-    protected $requestToPlugin;
+    private $requestToPlugin;
 
     /** @var callable */
-    protected $dummyMiddleware;
+    private $dummyMiddleware;
 
     public function setUp()
     {
diff --git a/module/Rest/test/Middleware/CrossDomainMiddlewareTest.php b/module/Rest/test/Middleware/CrossDomainMiddlewareTest.php
index aeacf156..bde89c6b 100644
--- a/module/Rest/test/Middleware/CrossDomainMiddlewareTest.php
+++ b/module/Rest/test/Middleware/CrossDomainMiddlewareTest.php
@@ -14,9 +14,9 @@ use Zend\Diactoros\ServerRequestFactory;
 class CrossDomainMiddlewareTest extends TestCase
 {
     /** @var CrossDomainMiddleware */
-    protected $middleware;
+    private $middleware;
     /** @var ObjectProphecy */
-    protected $delegate;
+    private $delegate;
 
     public function setUp()
     {
diff --git a/module/Rest/test/Middleware/PathVersionMiddlewareTest.php b/module/Rest/test/Middleware/PathVersionMiddlewareTest.php
index 14f41b61..7917962a 100644
--- a/module/Rest/test/Middleware/PathVersionMiddlewareTest.php
+++ b/module/Rest/test/Middleware/PathVersionMiddlewareTest.php
@@ -17,7 +17,7 @@ use function array_shift;
 class PathVersionMiddlewareTest extends TestCase
 {
     /** @var PathVersionMiddleware */
-    protected $middleware;
+    private $middleware;
 
     public function setUp()
     {
diff --git a/module/Rest/test/Service/ApiKeyServiceTest.php b/module/Rest/test/Service/ApiKeyServiceTest.php
index 78b8a8be..ae25c032 100644
--- a/module/Rest/test/Service/ApiKeyServiceTest.php
+++ b/module/Rest/test/Service/ApiKeyServiceTest.php
@@ -15,9 +15,9 @@ use Shlinkio\Shlink\Rest\Service\ApiKeyService;
 class ApiKeyServiceTest extends TestCase
 {
     /** @var ApiKeyService */
-    protected $service;
+    private $service;
     /** @var ObjectProphecy */
-    protected $em;
+    private $em;
 
     public function setUp()
     {