diff --git a/generator/src/ComposerJsonEditor.php b/generator/src/ComposerJsonEditor.php
index 8e3b76a5..7ff7a55c 100644
--- a/generator/src/ComposerJsonEditor.php
+++ b/generator/src/ComposerJsonEditor.php
@@ -1,5 +1,6 @@
 <?php
 
+declare(strict_types=1);
 
 namespace Safe;
 
diff --git a/generator/src/DeprecateCommand.php b/generator/src/DeprecateCommand.php
index 3f4dd56d..136f50be 100644
--- a/generator/src/DeprecateCommand.php
+++ b/generator/src/DeprecateCommand.php
@@ -1,5 +1,6 @@
 <?php
 
+declare(strict_types=1);
 
 namespace Safe;
 
@@ -23,7 +24,7 @@ protected function configure(): void
         ;
     }
 
-    protected function execute(InputInterface $input, OutputInterface $output)
+    protected function execute(InputInterface $input, OutputInterface $output): int
     {
         /** @var string $moduleName */
         $moduleName = $input->getArgument('module');
diff --git a/generator/src/DocPage.php b/generator/src/DocPage.php
index d55204e5..c202724b 100644
--- a/generator/src/DocPage.php
+++ b/generator/src/DocPage.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Safe;
 
 use function explode;
@@ -236,8 +238,6 @@ public function getMethodSynopsis(): array
 
     /**
      * Loads the XML file, resolving all DTD declared entities.
-     *
-     * @return \SimpleXMLElement
      */
     public function loadAndResolveFile(): \SimpleXMLElement
     {
@@ -268,8 +268,6 @@ public function loadAndResolveFile(): \SimpleXMLElement
 
     /**
      * Returns the module name in Camelcase.
-     *
-     * @return string
      */
     public function getModule(): string
     {
diff --git a/generator/src/EmptyTypeException.php b/generator/src/EmptyTypeException.php
index cf584eca..8ea96b82 100644
--- a/generator/src/EmptyTypeException.php
+++ b/generator/src/EmptyTypeException.php
@@ -1,5 +1,6 @@
 <?php
 
+declare(strict_types=1);
 
 namespace Safe;
 
diff --git a/generator/src/FileCreator.php b/generator/src/FileCreator.php
index 013b8b47..610cd107 100644
--- a/generator/src/FileCreator.php
+++ b/generator/src/FileCreator.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Safe;
 
 use Rector\Config\RectorConfig;
@@ -14,7 +16,6 @@ class FileCreator
      * This function generate an improved php lib function in a php file
      *
      * @param Method[] $functions
-     * @param string $path
      */
     public function generatePhpFile(array $functions, string $path): void
     {
@@ -64,7 +65,6 @@ private function getFunctionsNameList(array $functions): array
      * This function generate a PHP file containing the list of functions we can handle.
      *
      * @param Method[] $functions
-     * @param string $path
      */
     public function generateFunctionsList(array $functions, string $path): void
     {
@@ -86,7 +86,6 @@ public function generateFunctionsList(array $functions, string $path): void
      * Generates a configuration file for replacing all functions when using rector/rector.
      *
      * @param Method[] $functions
-     * @param string $path
      */
     public function generateRectorFile(array $functions, string $path): void
     {
@@ -148,9 +147,6 @@ public static function createFromPhpError(): self
 
     /**
      * Generates the name of the exception class
-     *
-     * @param string $moduleName
-     * @return string
      */
     public static function toExceptionName(string $moduleName): string
     {
diff --git a/generator/src/GenerateCommand.php b/generator/src/GenerateCommand.php
index 1cd505b7..4868a29d 100644
--- a/generator/src/GenerateCommand.php
+++ b/generator/src/GenerateCommand.php
@@ -1,5 +1,6 @@
 <?php
 
+declare(strict_types=1);
 
 namespace Safe;
 
@@ -18,7 +19,7 @@ protected function configure(): void
         ;
     }
 
-    protected function execute(InputInterface $input, OutputInterface $output)
+    protected function execute(InputInterface $input, OutputInterface $output): int
     {
 
         $this->rmGenerated();
diff --git a/generator/src/Method.php b/generator/src/Method.php
index d3406fd4..4f7b3418 100644
--- a/generator/src/Method.php
+++ b/generator/src/Method.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Safe;
 
 use Safe\PhpStanFunctions\PhpStanFunction;
@@ -26,14 +28,13 @@ class Method
     /**
      * @var Parameter[]|null
      */
-    private $params = null;
     /**
      * @var int
      */
     private $errorType;
+    private ?array $params = null;
     /**
      * The function prototype from the phpstan internal documentation (functionMap.php)
-     * @var PhpStanFunction|null
      */
     private $phpstanSignarure;
     /**
@@ -225,8 +226,6 @@ public function getModuleName(): string
 
     /**
      * The function is overloaded if at least one parameter is optional with no default value and this parameter is not by reference.
-     *
-     * @return bool
      */
     public function isOverloaded(): bool
     {
diff --git a/generator/src/Parameter.php b/generator/src/Parameter.php
index 27f86bf4..1708bbcb 100644
--- a/generator/src/Parameter.php
+++ b/generator/src/Parameter.php
@@ -1,4 +1,7 @@
 <?php
+
+declare(strict_types=1);
+
 namespace Safe;
 
 use Safe\PhpStanFunctions\PhpStanFunction;
@@ -58,8 +61,6 @@ public function isByReference(): bool
     /**
      * Some parameters can be optional with no default value. In this case, the function is "overloaded" (which is not
      * possible in user-land but possible in core...)
-     *
-     * @return bool
      */
     public function isOptionalWithNoDefault(): bool
     {
diff --git a/generator/src/PhpStanFunctions/PhpStanFunction.php b/generator/src/PhpStanFunctions/PhpStanFunction.php
index 7381f17a..720240a6 100644
--- a/generator/src/PhpStanFunctions/PhpStanFunction.php
+++ b/generator/src/PhpStanFunctions/PhpStanFunction.php
@@ -1,5 +1,6 @@
 <?php
 
+declare(strict_types=1);
 
 namespace Safe\PhpStanFunctions;
 
@@ -13,7 +14,7 @@ class PhpStanFunction
     /**
      * @var PhpStanParameter[]
      */
-    private $parameters = [];
+    private array $parameters = [];
 
     /**
      * @param string[] $signature
diff --git a/generator/src/PhpStanFunctions/PhpStanFunctionMapReader.php b/generator/src/PhpStanFunctions/PhpStanFunctionMapReader.php
index f6987fd1..a56076ea 100644
--- a/generator/src/PhpStanFunctions/PhpStanFunctionMapReader.php
+++ b/generator/src/PhpStanFunctions/PhpStanFunctionMapReader.php
@@ -1,5 +1,6 @@
 <?php
 
+declare(strict_types=1);
 
 namespace Safe\PhpStanFunctions;
 
diff --git a/generator/src/PhpStanFunctions/PhpStanParameter.php b/generator/src/PhpStanFunctions/PhpStanParameter.php
index 16deedaf..3d8e5e20 100644
--- a/generator/src/PhpStanFunctions/PhpStanParameter.php
+++ b/generator/src/PhpStanFunctions/PhpStanParameter.php
@@ -1,5 +1,6 @@
 <?php
 
+declare(strict_types=1);
 
 namespace Safe\PhpStanFunctions;
 
@@ -29,9 +30,6 @@ public function __construct(string $name, string $type)
         $this->type = new PhpStanType($type, $writeOnly);
     }
 
-    /**
-     * @return string
-     */
     public function getName(): string
     {
         return $this->name;
diff --git a/generator/src/PhpStanFunctions/PhpStanType.php b/generator/src/PhpStanFunctions/PhpStanType.php
index bf0e8fdb..814660e5 100644
--- a/generator/src/PhpStanFunctions/PhpStanType.php
+++ b/generator/src/PhpStanFunctions/PhpStanType.php
@@ -1,5 +1,6 @@
 <?php
 
+declare(strict_types=1);
 
 namespace Safe\PhpStanFunctions;
 
@@ -17,18 +18,15 @@ class PhpStanType
         '\OCI-Lob',
         '\OCI-Collection',
     ];
-    /**
-     * @var bool
-     */
-    private $nullable;
-    /**
-     * @var bool
-     */
-    private $falsable;
+
+    private bool $nullable;
+
+    private bool $falsable;
+
     /**
      * @var string[]
      */
-    private $types;
+    private array $types;
 
     public function __construct(string $data, bool $writeOnly = false)
     {
diff --git a/generator/src/ScanObjectsCommand.php b/generator/src/ScanObjectsCommand.php
index 330e08af..b0827235 100644
--- a/generator/src/ScanObjectsCommand.php
+++ b/generator/src/ScanObjectsCommand.php
@@ -1,5 +1,6 @@
 <?php
 
+declare(strict_types=1);
 
 namespace Safe;
 
@@ -17,7 +18,7 @@ protected function configure(): void
         ;
     }
 
-    protected function execute(InputInterface $input, OutputInterface $output)
+    protected function execute(InputInterface $input, OutputInterface $output): int
     {
         $scanner = new Scanner(__DIR__ . '/../doc/doc-en/en/reference/');
 
diff --git a/generator/src/Scanner.php b/generator/src/Scanner.php
index 67835752..38251054 100644
--- a/generator/src/Scanner.php
+++ b/generator/src/Scanner.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Safe;
 
 use function array_merge;
@@ -18,7 +20,7 @@ class Scanner
     /**
      * @var string[]
      */
-    private $ignoredFunctions;
+    private ?array $ignoredFunctions = null;
 
     /**
      * @var string[]
diff --git a/generator/src/ScannerResponse.php b/generator/src/ScannerResponse.php
index 647db147..e893cab7 100644
--- a/generator/src/ScannerResponse.php
+++ b/generator/src/ScannerResponse.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Safe;
 
 class ScannerResponse
diff --git a/generator/src/Type.php b/generator/src/Type.php
index b4569198..0751dc35 100644
--- a/generator/src/Type.php
+++ b/generator/src/Type.php
@@ -1,5 +1,6 @@
 <?php
 
+declare(strict_types=1);
 
 namespace Safe;
 
@@ -7,9 +8,6 @@ class Type
 {
     /**
      * Returns true if the type passed in parameter is a class, false if it is scalar or resource
-     *
-     * @param string $type
-     * @return bool
      */
     private static function isClass(string $type): bool
     {
diff --git a/generator/src/WritePhpFunction.php b/generator/src/WritePhpFunction.php
index f552aae3..d269ed37 100644
--- a/generator/src/WritePhpFunction.php
+++ b/generator/src/WritePhpFunction.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Safe;
 
 class WritePhpFunction
@@ -134,7 +136,6 @@ private function generateExceptionCode(string $moduleName, Method $method) : str
 
     /**
      * @param Parameter[] $params
-     * @return string
      */
     private function displayParamsWithType(array $params): string
     {
diff --git a/generator/tests/ComposerJsonEditorTest.php b/generator/tests/ComposerJsonEditorTest.php
index dc8b9441..a9d181b4 100644
--- a/generator/tests/ComposerJsonEditorTest.php
+++ b/generator/tests/ComposerJsonEditorTest.php
@@ -1,5 +1,6 @@
 <?php
 
+declare(strict_types=1);
 
 namespace Safe;
 
@@ -8,7 +9,7 @@
 
 class ComposerJsonEditorTest extends TestCase
 {
-    public function testFileListEditionForGeneration()
+    public function testFileListEditionForGeneration(): void
     {
         $oldList = [
             "deprecated/apc.php",
@@ -31,7 +32,7 @@ public function testFileListEditionForGeneration()
     }
     
     
-    public function testFileListEditionForDeprecation()
+    public function testFileListEditionForDeprecation(): void
     {
         $oldList = [
             "generated/apache.php",
diff --git a/generator/tests/DateTimeImmutableTest.php b/generator/tests/DateTimeImmutableTest.php
index b45ae343..d1da956d 100644
--- a/generator/tests/DateTimeImmutableTest.php
+++ b/generator/tests/DateTimeImmutableTest.php
@@ -1,5 +1,6 @@
 <?php
 
+declare(strict_types=1);
 
 namespace Safe;
 
@@ -132,7 +133,7 @@ public function testSub(): void
         $this->assertEquals($datetime->getTimestamp(), $safeDatime->getTimestamp());
     }
 
-    public function testSerialize()
+    public function testSerialize(): void
     {
         $timezone = new \DateTimeZone('Pacific/Chatham');
         $safeDatetime = DateTimeImmutable::createFromFormat('d-m-Y', '20-03-2006', $timezone);
diff --git a/generator/tests/DateTimeTest.php b/generator/tests/DateTimeTest.php
index ce4bf502..6f5b2d13 100644
--- a/generator/tests/DateTimeTest.php
+++ b/generator/tests/DateTimeTest.php
@@ -1,5 +1,6 @@
 <?php
 
+declare(strict_types=1);
 
 namespace Safe;
 
diff --git a/generator/tests/DeprecateCommandTest.php b/generator/tests/DeprecateCommandTest.php
index 2caf2548..6d631a77 100644
--- a/generator/tests/DeprecateCommandTest.php
+++ b/generator/tests/DeprecateCommandTest.php
@@ -1,5 +1,6 @@
 <?php
 
+declare(strict_types=1);
 
 namespace Safe;
 
@@ -8,7 +9,7 @@
 
 class DeprecateCommandTest extends TestCase
 {
-    public function testExceptionName()
+    public function testExceptionName(): void
     {
         $this->assertEquals('Exceptions/ApcException.php', DeprecateCommand::getExceptionFilePath('apc'));
     }
diff --git a/generator/tests/DocPageTest.php b/generator/tests/DocPageTest.php
index f8a1e7d6..842d932e 100644
--- a/generator/tests/DocPageTest.php
+++ b/generator/tests/DocPageTest.php
@@ -1,12 +1,14 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Safe;
 
 use PHPUnit\Framework\TestCase;
 
 class DocPageTest extends TestCase
 {
-    public function testDetectFalsyFunction()
+    public function testDetectFalsyFunction(): void
     {
         $pregMatch = new DocPage(__DIR__ . '/../doc/doc-en/en/reference/pcre/functions/preg-match.xml');
         $implode = new DocPage(__DIR__ . '/../doc/doc-en/en/reference/strings/functions/implode.xml');
@@ -35,14 +37,14 @@ public function testDetectFalsyFunction()
         $this->assertTrue($fopen->detectFalsyFunction());
     }
 
-    public function testDetectNullsyFunction()
+    public function testDetectNullsyFunction(): void
     {
         $implode = new DocPage(__DIR__ . '/../doc/doc-en/en/reference/strings/functions/implode.xml');
 
         $this->assertFalse($implode->detectNullsyFunction());
     }
 
-    public function testDetectEmptyFunction()
+    public function testDetectEmptyFunction(): void
     {
         $pgHost = new DocPage(__DIR__ . '/../doc/doc-en/en/reference/pgsql/functions/pg-host.xml');
 
diff --git a/generator/tests/GeneratedFilesTest.php b/generator/tests/GeneratedFilesTest.php
index 021c3b70..f165679e 100644
--- a/generator/tests/GeneratedFilesTest.php
+++ b/generator/tests/GeneratedFilesTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Safe;
 
 use PHPUnit\Framework\TestCase;
@@ -12,7 +14,7 @@
  */
 class GeneratedFilesTest extends TestCase
 {
-    public function testSprintf()
+    public function testSprintf(): void
     {
         require_once __DIR__ . '/../../generated/strings.php';
         require_once __DIR__ . '/../../lib/Exceptions/SafeExceptionInterface.php';
@@ -22,7 +24,7 @@ public function testSprintf()
         $this->assertSame('foobar', sprintf('foo%s', 'bar'));
         $this->assertSame('foobarbaz', sprintf('foo%s%s', 'bar', 'baz'));
 
-        set_error_handler(function () {
+        set_error_handler(function (): void {
         });
         try {
             $this->expectException(\ArgumentCountError::class);
@@ -32,7 +34,7 @@ public function testSprintf()
         }
     }
 
-    public function testPregMatch()
+    public function testPregMatch(): void
     {
         require_once __DIR__ . '/../../generated/pcre.php';
         require_once __DIR__ . '/../../lib/Exceptions/SafeExceptionInterface.php';
@@ -46,7 +48,7 @@ public function testPregMatch()
         $this->assertSame($originalMatches, $matches);
     }
 
-    public function testObjects()
+    public function testObjects(): void
     {
         require_once __DIR__ . '/../../lib/special_cases.php';
         require_once __DIR__ . '/../../lib/Exceptions/SafeExceptionInterface.php';
@@ -76,7 +78,7 @@ public function testObjects()
      * Tests that the limit parameter is nullable.
      * See https://github.com/thecodingmachine/safe/issues/56
      */
-    public function testPregSplit()
+    public function testPregSplit(): void
     {
         require_once __DIR__ . '/../../generated/pcre.php';
         require_once __DIR__ . '/../../lib/Exceptions/SafeExceptionInterface.php';
@@ -90,7 +92,7 @@ public function testPregSplit()
     /**
      * Tests that parameters with "time()" default value are correctly handled.
      */
-    public function testStrtotime()
+    public function testStrtotime(): void
     {
         require_once __DIR__ . '/../../generated/datetime.php';
         require_once __DIR__ . '/../../lib/Exceptions/SafeExceptionInterface.php';
@@ -98,7 +100,7 @@ public function testStrtotime()
 
         $this->assertSame(\strtotime('+1 day'), strtotime('+1 day'));
 
-        set_error_handler(function () {
+        set_error_handler(function (): void {
         });
         try {
             $this->expectException(DatetimeException::class);
@@ -111,7 +113,7 @@ public function testStrtotime()
     /**
      * Tests that parameters signature can be not passed. See https://github.com/thecodingmachine/safe/issues/86
      */
-    public function testOpenSslSign()
+    public function testOpenSslSign(): void
     {
         require_once __DIR__ . '/../../generated/openssl.php';
         require_once __DIR__ . '/../../lib/Exceptions/SafeExceptionInterface.php';
@@ -123,7 +125,7 @@ public function testOpenSslSign()
         $this->assertSame($signature, $signatureSafe);
     }
 
-    public function testOpenSslEncrypt()
+    public function testOpenSslEncrypt(): void
     {
         $result = \openssl_encrypt(
             'test',
diff --git a/generator/tests/MethodTest.php b/generator/tests/MethodTest.php
index 82723aae..0cfe4d4e 100644
--- a/generator/tests/MethodTest.php
+++ b/generator/tests/MethodTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Safe;
 
 use PHPUnit\Framework\TestCase;
@@ -7,7 +9,7 @@
 
 class MethodTest extends TestCase
 {
-    public function testGetFunctionName()
+    public function testGetFunctionName(): void
     {
         $docPage = new DocPage(__DIR__ . '/../doc/doc-en/en/reference/pcre/functions/preg-match.xml');
         $xmlObject = $docPage->getMethodSynopsis();
@@ -16,7 +18,7 @@ public function testGetFunctionName()
         $this->assertEquals('preg_match', $name);
     }
 
-    public function testGetFunctionType()
+    public function testGetFunctionType(): void
     {
         $docPage = new DocPage(__DIR__ . '/../doc/doc-en/en/reference/pcre/functions/preg-match.xml');
         $xmlObject = $docPage->getMethodSynopsis();
@@ -25,7 +27,7 @@ public function testGetFunctionType()
         $this->assertEquals('int', $type);
     }
 
-    public function testGetFunctionParam()
+    public function testGetFunctionParam(): void
     {
         $docPage = new DocPage(__DIR__ . '/../doc/doc-en/en/reference/pcre/functions/preg-match.xml');
         $xmlObject = $docPage->getMethodSynopsis();
@@ -35,7 +37,7 @@ public function testGetFunctionParam()
         $this->assertEquals('pattern', $params[0]->getParameterName());
     }
 
-    public function testGetTypeHintFromRessource()
+    public function testGetTypeHintFromResource(): void
     {
         $docPage = new DocPage(__DIR__ . '/../doc/doc-en/en/reference/strings/functions/sprintf.xml');
         $xmlObject = $docPage->getMethodSynopsis();
@@ -74,7 +76,7 @@ public function testGetTypeHintFromRessource()
         $this->assertEquals('\HashContext', $params[0]->getSignatureType());
     }
     
-    public function testImapOpen5Parameter()
+    public function testImapOpen5Parameter(): void
     {
         $docPage = new DocPage(__DIR__ . '/../doc/doc-en/en/reference/imap/functions/imap-open.xml');
         $xmlObject = $docPage->getMethodSynopsis();
@@ -84,7 +86,7 @@ public function testImapOpen5Parameter()
         $this->assertEquals('array', $params[5]->getSignatureType());        
     }
 
-    public function testGetInitializer()
+    public function testGetInitializer(): void
     {
         $docPage = new DocPage(__DIR__ . '/../doc/doc-en/en/reference/apache/functions/apache-getenv.xml');
         $xmlObject = $docPage->getMethodSynopsis();
diff --git a/generator/tests/PhpStanFunctions/PhpStanFunctionMapReaderTest.php b/generator/tests/PhpStanFunctions/PhpStanFunctionMapReaderTest.php
index 2af9fd3f..e6141016 100644
--- a/generator/tests/PhpStanFunctions/PhpStanFunctionMapReaderTest.php
+++ b/generator/tests/PhpStanFunctions/PhpStanFunctionMapReaderTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Safe\PhpStanFunctions;
 
 use PHPUnit\Framework\TestCase;
diff --git a/generator/tests/PhpStanFunctions/PhpStanTypeTest.php b/generator/tests/PhpStanFunctions/PhpStanTypeTest.php
index 6db4e257..4b6ff87d 100644
--- a/generator/tests/PhpStanFunctions/PhpStanTypeTest.php
+++ b/generator/tests/PhpStanFunctions/PhpStanTypeTest.php
@@ -1,5 +1,6 @@
 <?php
 
+declare(strict_types=1);
 
 namespace Safe\PhpStanFunctions;
 
diff --git a/generator/tests/ScannerTest.php b/generator/tests/ScannerTest.php
index 65babe38..f285ff46 100644
--- a/generator/tests/ScannerTest.php
+++ b/generator/tests/ScannerTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Safe;
 
 use PHPUnit\Framework\TestCase;
@@ -7,7 +9,7 @@
 class ScannerTest extends TestCase
 {
 
-    public function testGetMethodsPaths()
+    public function testGetMethodsPaths(): void
     {
         $scanner = new Scanner(__DIR__ . '/../doc/doc-en/en/reference/');
         $paths = $scanner->getFunctionsPaths();
@@ -16,7 +18,7 @@ public function testGetMethodsPaths()
         $this->assertArrayNotHasKey(__DIR__.'/../doc/doc-en/en/reference/spl/appenditerator/getarrayiterator.xml', $paths);
     }
 
-    public function testGetFunctionsPaths()
+    public function testGetFunctionsPaths(): void
     {
         $scanner = new Scanner(__DIR__ . '/../doc/doc-en/en/reference/');
         $paths = $scanner->getMethodsPaths();
diff --git a/generator/tests/SpecialCasesTest.php b/generator/tests/SpecialCasesTest.php
index e5f97232..b4f17d3c 100644
--- a/generator/tests/SpecialCasesTest.php
+++ b/generator/tests/SpecialCasesTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Safe;
 
 use PHPUnit\Framework\TestCase;
@@ -9,7 +11,7 @@
 class SpecialCasesTest extends TestCase
 {
 
-    public function testPregReplace()
+    public function testPregReplace(): void
     {
         require_once __DIR__.'/../../lib/special_cases.php';
         require_once __DIR__.'/../../lib/Exceptions/SafeExceptionInterface.php';
@@ -20,7 +22,7 @@ public function testPregReplace()
         preg_replace("/([\s,]+)/u", "foo", "\xc3\x28");
     }
 
-    public function testFgetcsvWithTrailingNewline()
+    public function testFgetcsvWithTrailingNewline(): void
     {
         require_once __DIR__.'/../../lib/special_cases.php';
         require_once __DIR__.'/../../lib/Exceptions/SafeExceptionInterface.php';
@@ -37,7 +39,7 @@ public function testFgetcsvWithTrailingNewline()
         \fclose($handle);
     }
 
-    public function testFgetcsvReturnFalseonEndOfFile()
+    public function testFgetcsvReturnFalseonEndOfFile(): void
     {
         require_once __DIR__.'/../../lib/special_cases.php';
         require_once __DIR__.'/../../lib/Exceptions/SafeExceptionInterface.php';
diff --git a/generator/tests/TypeTest.php b/generator/tests/TypeTest.php
index d2f69e6d..aecfaa6e 100644
--- a/generator/tests/TypeTest.php
+++ b/generator/tests/TypeTest.php
@@ -1,12 +1,14 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Safe;
 
 use PHPUnit\Framework\TestCase;
 
 class TypeTest extends TestCase
 {
-    public function testIsClass()
+    public function testIsClass(): void
     {
         $this->assertSame('\\stdClass', Type::toRootNamespace('stdClass'));
         $this->assertSame('\\SimpleXMLElement', Type::toRootNamespace('SimpleXMLElement'));
diff --git a/generator/tests/rector/src/test.php b/generator/tests/rector/src/test.php
index 61b4bee7..5cb4b09a 100644
--- a/generator/tests/rector/src/test.php
+++ b/generator/tests/rector/src/test.php
@@ -1,3 +1,5 @@
 <?php
 
+declare(strict_types=1);
+
 glob('*');
diff --git a/generator/tests/rector/tests/RectorTest.php b/generator/tests/rector/tests/RectorTest.php
index 75bd940e..ada1be06 100644
--- a/generator/tests/rector/tests/RectorTest.php
+++ b/generator/tests/rector/tests/RectorTest.php
@@ -1,10 +1,12 @@
 <?php
 
+declare(strict_types=1);
+
 use PHPUnit\Framework\TestCase;
 
 final class RectorTest extends TestCase
 {
-    public function testRectorSucceeded()
+    public function testRectorSucceeded(): void
     {
         $content = file_get_contents(__DIR__.'/../src/test.php');
 
diff --git a/tests/DateTimeImmutableTest.php b/tests/DateTimeImmutableTest.php
index bfd207d5..21782ee4 100644
--- a/tests/DateTimeImmutableTest.php
+++ b/tests/DateTimeImmutableTest.php
@@ -29,7 +29,7 @@ public function testCreateFromInterface(\DateTimeInterface $dateTime): void
         self::assertSame($dateTime->format(\DATE_ATOM), $safeImmutableDate->format(\DATE_ATOM));
     }
 
-    public function createFromInterfaces(): array
+    public static function createFromInterfaces(): array
     {
         return [
             [new \DateTime('2022-11-29T14:17:34+00:00')],