diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 3f733be..d5ce722 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -8,10 +8,10 @@ jobs:
         runs-on: ubuntu-latest
         strategy:
             matrix:
-                php-versions: [ '7.2', '7.3', '7.4', '8.0' ]
+                php-versions: [ '7.2', '7.3', '7.4', '8.0', '8.1', '8.2' ]
         steps:
             -   name: Setup PHP, with composer and extensions
-                uses: shivammathur/setup-php@v1
+                uses: shivammathur/setup-php@v2
                 with:
                     php-version: ${{ matrix.php-versions }}
 
diff --git a/composer.json b/composer.json
index 5ee91b4..c4103ac 100644
--- a/composer.json
+++ b/composer.json
@@ -29,7 +29,7 @@
     },
     "require-dev": {
         "phpunit/phpunit": "^8.5",
-        "phpstan/phpstan": "^0.12.3"
+        "phpstan/phpstan": "^1.0"
     },
     "autoload": {
         "psr-4": {
diff --git a/src/Command/SearchCommand.php b/src/Command/SearchCommand.php
index 8e727ce..4c4a890 100644
--- a/src/Command/SearchCommand.php
+++ b/src/Command/SearchCommand.php
@@ -38,6 +38,7 @@ protected function doExecute(InputInterface $input, OutputInterface $output): in
     private function searchForPackage(): PackageInterface
     {
         $searchedPackage = $this->io->ask('What package do you want to lookup ? (TIP: you could also enter a part of a package name)');
+        assert(is_string($searchedPackage));
         $suggestedPackages = $this->suggestPackages((string)$searchedPackage);
 
         if ($suggestedPackages->isEmpty()) {
@@ -59,6 +60,7 @@ private function searchForPackage(): PackageInterface
         ));
 
         $choice = $this->io->choice('What package would you like to view ?', $options);
+        assert(is_string($choice));
 
         if (null !== $choice && 'Search again' !== $choice) {
             return $this->graph->getPackage($choice);
diff --git a/src/Composer/PackageDefinition.php b/src/Composer/PackageDefinition.php
index 752c862..6180043 100644
--- a/src/Composer/PackageDefinition.php
+++ b/src/Composer/PackageDefinition.php
@@ -31,6 +31,7 @@ public function __construct(array $definition, string $source)
     public static function createFromFile(SplFileInfo $file): self
     {
         $definition = json_decode($file->getContents(), true);
+        assert(is_array($definition));
 
         return new PackageDefinition($definition, $file->getPath());
     }
@@ -56,7 +57,10 @@ public function getPackageDirectory(): string
      */
     public function getAuthors(): array
     {
-        return $this->definition['authors'] ?? [];
+        $authors = $this->definition['authors'] ?? [];
+        assert(is_array($authors));
+
+        return $authors;
     }
 
     /**
@@ -64,7 +68,10 @@ public function getAuthors(): array
      */
     public function getDependencies(): array
     {
-        return $this->definition['require'] ?? [];
+        $dependencies = $this->definition['require'] ?? [];
+        assert(is_array($dependencies));
+
+        return $dependencies;
     }
 
     /**
@@ -72,7 +79,10 @@ public function getDependencies(): array
      */
     public function getDevDependencies(): array
     {
-        return $this->definition['require-dev'] ?? [];
+        $dependencies = $this->definition['require-dev'] ?? [];
+        assert(is_array($dependencies));
+
+        return $dependencies;
     }
 
     /**
@@ -80,6 +90,9 @@ public function getDevDependencies(): array
      */
     public function getReplaces(): array
     {
-        return $this->definition['replace'] ?? [];
+        $replace = $this->definition['replace'] ?? [];
+        assert(is_array($replace));
+
+        return $replace;
     }
 }
diff --git a/tests/Author/AuthorCollectionTest.php b/tests/Author/AuthorCollectionTest.php
index 8ae24fd..cbc2e63 100644
--- a/tests/Author/AuthorCollectionTest.php
+++ b/tests/Author/AuthorCollectionTest.php
@@ -7,7 +7,7 @@
 use Nusje2000\DependencyGraph\Author\Author;
 use Nusje2000\DependencyGraph\Author\AuthorCollection;
 use Nusje2000\DependencyGraph\Exception\AuthorException;
-use PHPStan\Testing\TestCase;
+use PHPUnit\Framework\TestCase;
 
 final class AuthorCollectionTest extends TestCase
 {
diff --git a/tests/Composer/PackageDefinitionTest.php b/tests/Composer/PackageDefinitionTest.php
index e83fa87..cad299d 100644
--- a/tests/Composer/PackageDefinitionTest.php
+++ b/tests/Composer/PackageDefinitionTest.php
@@ -6,7 +6,7 @@
 
 use Nusje2000\DependencyGraph\Composer\PackageDefinition;
 use Nusje2000\DependencyGraph\Exception\DefinitionException;
-use PHPStan\Testing\TestCase;
+use PHPUnit\Framework\TestCase;
 use Symfony\Component\Finder\SplFileInfo;
 
 final class PackageDefinitionTest extends TestCase
diff --git a/tests/Replace/ReplaceCollectionTest.php b/tests/Replace/ReplaceCollectionTest.php
index f506f38..4343274 100644
--- a/tests/Replace/ReplaceCollectionTest.php
+++ b/tests/Replace/ReplaceCollectionTest.php
@@ -7,7 +7,7 @@
 use Nusje2000\DependencyGraph\Exception\ReplaceException;
 use Nusje2000\DependencyGraph\Replace\Replace;
 use Nusje2000\DependencyGraph\Replace\ReplaceCollection;
-use PHPStan\Testing\TestCase;
+use PHPUnit\Framework\TestCase;
 
 final class ReplaceCollectionTest extends TestCase
 {