diff --git a/.github/workflows/phpstan-6.yaml b/.github/workflows/phpstan-6.yaml
deleted file mode 100644
index a367107..0000000
--- a/.github/workflows/phpstan-6.yaml
+++ /dev/null
@@ -1,23 +0,0 @@
-name: PHPStan level 6
-on: push
-jobs:
-  phpstan:
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v3
-      - uses: actions/cache@v3
-        with:
-          path: '**/vendor'
-          key: ${{ runner.os }}-composer-${{ hashFiles('**/composer.lock') }}
-          restore-keys: |
-            ${{ runner.os }}-composer-
-      - uses: php-actions/composer@v6
-        with:
-          args: --prefer-dist
-          php_version: '8.2'
-      - name: PHPStan
-        uses: php-actions/phpstan@v3
-        with:
-          path: src/
-          level: 6
-          php_version: '8.2'
diff --git a/.github/workflows/phpstan-7.yaml b/.github/workflows/phpstan-7.yaml
deleted file mode 100644
index cad733d..0000000
--- a/.github/workflows/phpstan-7.yaml
+++ /dev/null
@@ -1,23 +0,0 @@
-name: PHPStan level 7
-on: push
-jobs:
-  phpstan:
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v3
-      - uses: actions/cache@v3
-        with:
-          path: '**/vendor'
-          key: ${{ runner.os }}-composer-${{ hashFiles('**/composer.lock') }}
-          restore-keys: |
-            ${{ runner.os }}-composer-
-      - uses: php-actions/composer@v6
-        with:
-          args: --prefer-dist
-          php_version: '8.2'
-      - name: PHPStan
-        uses: php-actions/phpstan@v3
-        with:
-          path: src/
-          level: 7
-          php_version: '8.2'
diff --git a/.github/workflows/phpstan-8.yaml b/.github/workflows/phpstan-8.yaml
deleted file mode 100644
index 8d7aec6..0000000
--- a/.github/workflows/phpstan-8.yaml
+++ /dev/null
@@ -1,23 +0,0 @@
-name: PHPStan level 8
-on: push
-jobs:
-  phpstan:
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v3
-      - uses: actions/cache@v3
-        with:
-          path: '**/vendor'
-          key: ${{ runner.os }}-composer-${{ hashFiles('**/composer.lock') }}
-          restore-keys: |
-            ${{ runner.os }}-composer-
-      - uses: php-actions/composer@v6
-        with:
-          args: --prefer-dist
-          php_version: '8.2'
-      - name: PHPStan
-        uses: php-actions/phpstan@v3
-        with:
-          path: src/
-          level: 8
-          php_version: '8.2'
diff --git a/.github/workflows/phpstan-5.yaml b/.github/workflows/phpstan-9.yaml
similarity index 93%
rename from .github/workflows/phpstan-5.yaml
rename to .github/workflows/phpstan-9.yaml
index 906b4c9..9e64ec4 100644
--- a/.github/workflows/phpstan-5.yaml
+++ b/.github/workflows/phpstan-9.yaml
@@ -1,4 +1,4 @@
-name: PHPStan level 5
+name: PHPStan level 9
 on: push
 jobs:
   phpstan:
@@ -19,5 +19,5 @@ jobs:
         uses: php-actions/phpstan@v3
         with:
           path: src/
-          level: 5
+          level: 9
           php_version: '8.2'
diff --git a/.github/workflows/quality.yaml b/.github/workflows/quality.yaml
index 7457967..c3e2001 100644
--- a/.github/workflows/quality.yaml
+++ b/.github/workflows/quality.yaml
@@ -1,4 +1,4 @@
-name: Quality
+name: Quality (PHPSpec level 8)
 on: push
 jobs:
   cs-fixer:
@@ -34,5 +34,5 @@ jobs:
         uses: php-actions/phpstan@v3
         with:
           path: src/
-          level: 3
+          level: 8
           php_version: '8.2'
diff --git a/src/BuilderTestCase.php b/src/BuilderTestCase.php
index 632b71e..49488f6 100644
--- a/src/BuilderTestCase.php
+++ b/src/BuilderTestCase.php
@@ -25,6 +25,10 @@ protected function tearDown(): void
 
     protected function getBuilderCompilePath(): string
     {
+        if ($this->fs === null) {
+            throw new \RuntimeException('The virtual file system was not initialized. The '.__METHOD__.' method should be called after the '.get_class($this).'::setUp() method was called and after the '.get_class($this).'::tearDown() method is called.');
+        }
+
         return $this->fs->url();
     }
 
diff --git a/src/Constraint/Pipeline/PipelineExtractsLike.php b/src/Constraint/Pipeline/PipelineExtractsLike.php
index 2c57f46..16d4aa1 100644
--- a/src/Constraint/Pipeline/PipelineExtractsLike.php
+++ b/src/Constraint/Pipeline/PipelineExtractsLike.php
@@ -4,6 +4,7 @@
 
 namespace Kiboko\Component\PHPUnitExtension\Constraint\Pipeline;
 
+use Kiboko\Contract\Bucket\ResultBucketInterface;
 use Kiboko\Contract\Pipeline\ExtractorInterface;
 use Kiboko\Contract\Pipeline\NullStepRejection;
 use Kiboko\Contract\Pipeline\NullStepState;
@@ -26,9 +27,11 @@ public function __construct(
     }
 
     /**
-     * @param list<Type> $iterable
+     * @template ItemType
      *
-     * @return \Iterator<Type>
+     * @param list<ItemType> $iterable
+     *
+     * @return \Iterator<ItemType>
      */
     private function asIterator(iterable $iterable): \Iterator
     {
diff --git a/src/Mock/ApiClientMockBuilder.php b/src/Mock/ApiClientMockBuilder.php
index b798260..1be4b69 100644
--- a/src/Mock/ApiClientMockBuilder.php
+++ b/src/Mock/ApiClientMockBuilder.php
@@ -17,7 +17,7 @@ final class ApiClientMockBuilder implements Builder
     /** @param array<Node\Arg|Node\VariadicPlaceholder> $mockedArgs */
     public function __construct(
         private readonly string $mockedClientBuilder,
-        private readonly ?array $mockedArgs = []
+        private readonly array $mockedArgs = []
     ) {
         $this->node = new Node\Expr\New_(
             class: new Node\Name\FullyQualified($this->mockedClientBuilder),