diff --git a/composer.json b/composer.json
index d0dd2bd..85fe63d 100644
--- a/composer.json
+++ b/composer.json
@@ -38,9 +38,8 @@
         "amphp/http-client": "To use the web test case trait"
     },
     "require-dev": {
-        "amphp/http-client": "^5.0.1",
         "friendsofphp/php-cs-fixer": "^3.53.0",
-        "phpstan/phpstan": "^1.10"
+        "phpstan/phpstan": "^1.10.67"
     },
     "conflict": {
         "amphp/http-client": "<5.0.1",
diff --git a/phpstan.neon b/phpstan.neon
new file mode 100644
index 0000000..dff4656
--- /dev/null
+++ b/phpstan.neon
@@ -0,0 +1,6 @@
+parameters:
+    level: max
+    paths:
+        - src/
+    excludePaths:
+        - src/Assert/Assertion.php
\ No newline at end of file
diff --git a/src/Assert/Assertion.php b/src/Assert/Assertion.php
index 93937af..df136c8 100644
--- a/src/Assert/Assertion.php
+++ b/src/Assert/Assertion.php
@@ -5,7 +5,6 @@
 namespace Asynit\Assert;
 
 use Asynit\Runner\TestStorage;
-use Asynit\Test;
 use bovigo\assert\Assertion as BaseAssertion;
 use bovigo\assert\AssertionFailure;
 use bovigo\assert\predicate\Predicate;
diff --git a/src/Command/AsynitCommand.php b/src/Command/AsynitCommand.php
index 301615e..b5e1e23 100644
--- a/src/Command/AsynitCommand.php
+++ b/src/Command/AsynitCommand.php
@@ -14,7 +14,10 @@
 use Symfony\Component\Console\Input\InputOption;
 use Symfony\Component\Console\Output\OutputInterface;
 
-class AsynitCommand extends Command
+/**
+ * @internal
+ */
+final class AsynitCommand extends Command
 {
     private string $defaultBootstrapFilename = '';
 
@@ -45,22 +48,40 @@ protected function execute(InputInterface $input, OutputInterface $output): int
             throw new \InvalidArgumentException("The bootstrap file '$bootstrapFilename' does not exist.");
         }
 
+        /** @var string $target */
+        $target = $input->getArgument('target');
+
         $testsFinder = new TestsFinder();
-        $testMethods = $testsFinder->findTests($input->getArgument('target'));
+        $testsSuites = $testsFinder->findTests($target);
+        $testsCount = array_reduce($testsSuites, fn (int $carry, $suite) => $carry + \count($suite->tests), 0);
+
+        /** @phpstan-ignore-next-line */
+        $useOrder = (boolean) $input->getOption('order');
+
+        list($chainOutput, $countOutput) = (new OutputFactory($useOrder))->buildOutput($testsCount);
 
-        list($chainOutput, $countOutput) = (new OutputFactory($input->getOption('order')))->buildOutput(\count($testMethods));
+        /** @phpstan-ignore-next-line */
+        $timeout = (float) $input->getOption('timeout');
+        /** @phpstan-ignore-next-line */
+        $retry = (int) $input->getOption('retry');
+        /** @phpstan-ignore-next-line */
+        $concurrency = (int) $input->getOption('concurrency');
+
+        if ($concurrency < 1) {
+            throw new \InvalidArgumentException('Concurrency must be greater than 0');
+        }
 
         $defaultHttpConfiguration = new HttpClientConfiguration(
-            timeout: $input->getOption('timeout'),
-            retry: $input->getOption('retry'),
+            timeout: $timeout,
+            retry: $retry,
             allowSelfSignedCertificate: $input->hasOption('allow-self-signed-certificate'),
         );
 
         $builder = new TestPoolBuilder();
-        $runner = new PoolRunner($defaultHttpConfiguration, new TestWorkflow($chainOutput), $input->getOption('concurrency'));
+        $runner = new PoolRunner($defaultHttpConfiguration, new TestWorkflow($chainOutput), $concurrency);
 
         // Build a list of tests from the directory
-        $pool = $builder->build($testMethods);
+        $pool = $builder->build($testsSuites);
         $runner->loop($pool);
 
         // Return the number of failed tests
diff --git a/src/HttpClient/ApiResponse.php b/src/HttpClient/ApiResponse.php
index 2d5b0e8..04b77d0 100644
--- a/src/HttpClient/ApiResponse.php
+++ b/src/HttpClient/ApiResponse.php
@@ -14,7 +14,7 @@ class ApiResponse extends HttpResponse implements \ArrayAccess
     /**
      * @var array<string, mixed>|null
      */
-    private ?array $data = null;
+    private mixed $data = null;
 
     public function __construct(private readonly Response $response)
     {
@@ -24,7 +24,13 @@ public function __construct(private readonly Response $response)
     private function ensureBodyIsRead(bool $associative = true): void
     {
         if (null === $this->data) {
-            $this->data = json_decode($this->response->getBody()->read(), $associative, flags: JSON_THROW_ON_ERROR);
+            $data = json_decode((string) $this->response->getBody(), $associative, flags: JSON_THROW_ON_ERROR);
+
+            if (!is_array($data)) {
+                throw new \InvalidArgumentException('The response body is not a valid JSON object.');
+            }
+
+            $this->data = $data;
         }
     }
 
diff --git a/src/Output/Chain.php b/src/Output/Chain.php
index 05d4e84..b33c27a 100644
--- a/src/Output/Chain.php
+++ b/src/Output/Chain.php
@@ -9,38 +9,38 @@
 class Chain implements OutputInterface
 {
     /** @var OutputInterface[] */
-    private $outputs = [];
+    private array $outputs = [];
 
     /**
      * Add output to the chain.
      */
-    public function addOutput(OutputInterface $output)
+    public function addOutput(OutputInterface $output): void
     {
         $this->outputs[] = $output;
     }
 
-    public function outputStep(Test $test, $debugOutput)
+    public function outputStep(Test $test, string $debugOutput): void
     {
         foreach ($this->outputs as $output) {
             $output->outputStep($test, $debugOutput);
         }
     }
 
-    public function outputFailure(Test $test, $debugOutput, $failure)
+    public function outputFailure(Test $test, string $debugOutput, \Throwable $failure): void
     {
         foreach ($this->outputs as $output) {
             $output->outputFailure($test, $debugOutput, $failure);
         }
     }
 
-    public function outputSuccess(Test $test, $debugOutput)
+    public function outputSuccess(Test $test, string $debugOutput): void
     {
         foreach ($this->outputs as $output) {
             $output->outputSuccess($test, $debugOutput);
         }
     }
 
-    public function outputSkipped(Test $test, $debugOutput)
+    public function outputSkipped(Test $test, string $debugOutput): void
     {
         foreach ($this->outputs as $output) {
             $output->outputSkipped($test, $debugOutput);
diff --git a/src/Output/Count.php b/src/Output/Count.php
index 74b39e4..303c9ef 100644
--- a/src/Output/Count.php
+++ b/src/Output/Count.php
@@ -8,41 +8,35 @@
 
 class Count implements OutputInterface
 {
-    private $succeed = 0;
-    private $failed = 0;
-    private $skipped = 0;
+    private int $succeed = 0;
+    private int $failed = 0;
+    private int $skipped = 0;
 
-    public function outputStep(Test $test, $debugOutput)
+    public function outputStep(Test $test, string $debugOutput): void
     {
     }
 
-    public function outputFailure(Test $test, $debugOutput, $failure)
+    public function outputFailure(Test $test, string $debugOutput, \Throwable $failure): void
     {
         ++$this->failed;
     }
 
-    public function outputSuccess(Test $test, $debugOutput)
+    public function outputSuccess(Test $test, string $debugOutput): void
     {
         ++$this->succeed;
     }
 
-    public function outputSkipped(Test $test, $debugOutput)
+    public function outputSkipped(Test $test, string $debugOutput): void
     {
         ++$this->skipped;
     }
 
-    /**
-     * @return int
-     */
-    public function getSucceed()
+    public function getSucceed(): int
     {
         return $this->succeed;
     }
 
-    /**
-     * @return int
-     */
-    public function getFailed()
+    public function getFailed(): int
     {
         return $this->failed;
     }
diff --git a/src/Output/OutputFactory.php b/src/Output/OutputFactory.php
index 0fb8966..198084a 100644
--- a/src/Output/OutputFactory.php
+++ b/src/Output/OutputFactory.php
@@ -6,16 +6,18 @@
 
 /**
  * Allow to detect current environment and choose the best output.
+ *
+ * @internal
  */
-class OutputFactory
+final class OutputFactory
 {
-    private $order = false;
-
-    public function __construct(bool $order = false)
+    public function __construct(public readonly bool $order = false)
     {
-        $this->order = $order;
     }
 
+    /**
+     * @return array{Chain, Count}
+     */
     public function buildOutput(int $testCount): array
     {
         $countOutput = new Count();
diff --git a/src/Output/OutputInterface.php b/src/Output/OutputInterface.php
index 589a569..ef6c230 100644
--- a/src/Output/OutputInterface.php
+++ b/src/Output/OutputInterface.php
@@ -6,18 +6,16 @@
 
 /**
  * Interface for displaying tests.
+ *
+ * @internal
  */
 interface OutputInterface
 {
-    public function outputStep(Test $test, $debugOutput);
+    public function outputStep(Test $test, string $debugOutput): void;
 
-    /**
-     * @param string                $debugOutput
-     * @param \Throwable|\Exception $failure
-     */
-    public function outputFailure(Test $test, $debugOutput, $failure);
+    public function outputFailure(Test $test, string $debugOutput, \Throwable $failure): void;
 
-    public function outputSuccess(Test $test, $debugOutput);
+    public function outputSuccess(Test $test, string $debugOutput): void;
 
-    public function outputSkipped(Test $test, $debugOutput);
+    public function outputSkipped(Test $test, string $debugOutput): void;
 }
diff --git a/src/Output/OutputOrder.php b/src/Output/OutputOrder.php
index 55317d3..7f3135b 100644
--- a/src/Output/OutputOrder.php
+++ b/src/Output/OutputOrder.php
@@ -7,23 +7,23 @@
 class OutputOrder implements OutputInterface
 {
     /** @var Test[] */
-    private $tests = [];
+    private array $tests = [];
 
-    public function outputStep(Test $test, $debugOutput)
+    public function outputStep(Test $test, string $debugOutput): void
     {
     }
 
-    public function outputFailure(Test $test, $debugOutput, $failure)
+    public function outputFailure(Test $test, string $debugOutput, \Throwable $failure): void
     {
         $this->tests[] = $test;
     }
 
-    public function outputSuccess(Test $test, $debugOutput)
+    public function outputSuccess(Test $test, string $debugOutput): void
     {
         $this->tests[] = $test;
     }
 
-    public function outputSkipped(Test $test, $debugOutput)
+    public function outputSkipped(Test $test, string $debugOutput): void
     {
     }
 
@@ -48,6 +48,11 @@ public function __destruct()
         }
     }
 
+    /**
+     * @param array<string, int> $orders
+     *
+     * @return int[]
+     */
     public function createDepends(Test $test, array $orders = []): array
     {
         $depends = [];
diff --git a/src/Output/PhpUnitAlike.php b/src/Output/PhpUnitAlike.php
index f80ed86..3f4905f 100644
--- a/src/Output/PhpUnitAlike.php
+++ b/src/Output/PhpUnitAlike.php
@@ -10,14 +10,15 @@ class PhpUnitAlike implements OutputInterface
     public const SPLIT_AT = 60;
     public const MAX_TRACE = 10;
 
-    private $outputFormatFail;
-    private $outputFormatSuccess;
-    private $outputFormatSkipped;
-    private $testOutputed;
-    private $failures;
-    private $assertionCount;
-    private $start;
-    private $testCount;
+    private OutputFormatterStyle $outputFormatFail;
+    private OutputFormatterStyle $outputFormatSuccess;
+    private OutputFormatterStyle $outputFormatSkipped;
+    private int $testOutputed;
+    /** @var array<array{test: Test, failure: \Throwable}> */
+    private array $failures;
+    private int $assertionCount;
+    private float $start;
+    private int $testCount;
 
     public function __construct(int $testCount)
     {
@@ -34,11 +35,11 @@ public function __construct(int $testCount)
         $this->failures = [];
     }
 
-    public function outputStep(Test $test, $debugOutput)
+    public function outputStep(Test $test, string $debugOutput): void
     {
     }
 
-    public function outputFailure(Test $test, $debugOutput, $failure)
+    public function outputFailure(Test $test, string $debugOutput, \Throwable $failure): void
     {
         $text = 'F';
 
@@ -57,7 +58,7 @@ public function outputFailure(Test $test, $debugOutput, $failure)
         ];
     }
 
-    public function outputSuccess(Test $test, $debugOutput)
+    public function outputSuccess(Test $test, string $debugOutput): void
     {
         $this->writeTest($test, $this->outputFormatSuccess->apply('.'));
         fwrite(STDOUT, $debugOutput);
@@ -65,7 +66,7 @@ public function outputSuccess(Test $test, $debugOutput)
         $this->assertionCount += \count($test->getAssertions());
     }
 
-    public function outputSkipped(Test $test, $debugOutput)
+    public function outputSkipped(Test $test, string $debugOutput): void
     {
         $this->writeTest($test, $this->outputFormatSkipped->apply('S'));
         fwrite(STDOUT, $debugOutput);
@@ -73,7 +74,7 @@ public function outputSkipped(Test $test, $debugOutput)
         $this->assertionCount += \count($test->getAssertions());
     }
 
-    private function writeTest(Test $test, $text)
+    private function writeTest(Test $test, string $text): void
     {
         if (!$test->isRealTest) {
             return;
@@ -89,7 +90,7 @@ private function writeTest(Test $test, $text)
         ++$this->testOutputed;
     }
 
-    private function writeFailure($step, Test $test, $failure)
+    private function writeFailure(int $step, Test $test, \Throwable $failure): void
     {
         fwrite(STDOUT, $step + 1 .') '.$test->getDisplayName()." failed\n");
 
@@ -143,7 +144,7 @@ public function __destruct()
         fwrite(STDOUT, $outputFormatSuccess->apply("OK, Tests: $this->testOutputed, Assertions: $this->assertionCount.\n"));
     }
 
-    private function getDisplayableMemory($memory)
+    private function getDisplayableMemory(int $memory): string
     {
         $unit = ['B', 'KB', 'MB', 'GB', 'TB', 'PB'];
 
diff --git a/src/Parser/TestPoolBuilder.php b/src/Parser/TestPoolBuilder.php
index 8f82bb8..c9a41eb 100644
--- a/src/Parser/TestPoolBuilder.php
+++ b/src/Parser/TestPoolBuilder.php
@@ -6,6 +6,7 @@
 use Asynit\Attribute\DisplayName;
 use Asynit\Pool;
 use Asynit\Test;
+use Asynit\TestSuite;
 
 /**
  * Build test.
@@ -15,19 +16,26 @@ final class TestPoolBuilder
     /**
      * Build the initial test pool.
      *
-     * @param Test[] $tests
+     * @param TestSuite<object>[] $testSuites
      *
      * @throws \RuntimeException
      */
-    public function build(array $tests): Pool
+    public function build(array $testSuites): Pool
     {
         $pool = new Pool();
 
-        $tests = new \ArrayObject($tests);
+        /** @var \ArrayObject<string, Test> $tests */
+        $tests = new \ArrayObject();
+
+        foreach ($testSuites as $testSuite) {
+            foreach ($testSuite->tests as $test) {
+                $tests[$test->getIdentifier()] = $test;
+            }
+        }
 
         foreach ($tests as $test) {
             $this->processTestAnnotations($tests, $test);
-            $pool->addTest($test);
+            $pool->tests[] = $test;
         }
 
         return $pool;
diff --git a/src/Parser/TestsFinder.php b/src/Parser/TestsFinder.php
index a9b7992..b46b09b 100644
--- a/src/Parser/TestsFinder.php
+++ b/src/Parser/TestsFinder.php
@@ -5,11 +5,15 @@
 use Asynit\Attribute\Test as TestAnnotation;
 use Asynit\Attribute\TestCase;
 use Asynit\Test;
+use Asynit\TestSuite;
 use Symfony\Component\Finder\Finder;
 
-class TestsFinder
+/**
+ * @internal
+ */
+final class TestsFinder
 {
-    /** @return Test[] */
+    /** @return TestSuite<object>[] */
     public function findTests(string $path): array
     {
         if (\is_file($path)) {
@@ -28,13 +32,11 @@ public function findTests(string $path): array
     /**
      * @param iterable<string|\SplFileInfo> $files
      *
-     * @return Test[]
-     *
-     * @throws \ReflectionException
+     * @return TestSuite<object>[]
      */
     private function doFindTests(iterable $files): array
     {
-        $methods = [];
+        $suites = [];
 
         foreach ($files as $file) {
             $existingClasses = get_declared_classes();
@@ -56,6 +58,9 @@ private function doFindTests(iterable $files): array
                     continue;
                 }
 
+                $testSuite = new TestSuite($reflectionClass);
+                $suites[] = $testSuite;
+
                 foreach ($reflectionClass->getMethods(\ReflectionMethod::IS_PUBLIC) as $reflectionMethod) {
                     $tests = $reflectionMethod->getAttributes(TestAnnotation::class);
                     $test = null;
@@ -67,12 +72,12 @@ private function doFindTests(iterable $files): array
                     }
 
                     if (null !== $test) {
-                        $methods[$test->getIdentifier()] = $test;
+                        $testSuite->tests[$test->getIdentifier()] = $test;
                     }
                 }
             }
         }
 
-        return $methods;
+        return $suites;
     }
 }
diff --git a/src/Pool.php b/src/Pool.php
index fc31207..d11806e 100644
--- a/src/Pool.php
+++ b/src/Pool.php
@@ -4,24 +4,13 @@
 
 /**
  * Pool containing test, running tests and running http calls.
+ *
+ * @internal
  */
-class Pool
+final class Pool
 {
     /** @var Test[] */
-    private $tests;
-
-    public function __construct()
-    {
-        $this->tests = [];
-    }
-
-    /**
-     * Queue a test.
-     */
-    public function addTest(Test $test): void
-    {
-        $this->tests[] = $test;
-    }
+    public array $tests = [];
 
     public function isEmpty(): bool
     {
@@ -32,7 +21,7 @@ public function isEmpty(): bool
         return 0 === count($notCompletedTests);
     }
 
-    public function getTestToRun(): ?Test
+    public function getNextTestToRun(): ?Test
     {
         foreach ($this->tests as $test) {
             if ($test->canBeRun()) {
diff --git a/src/Runner/PoolRunner.php b/src/Runner/PoolRunner.php
index fbbacd8..ab72e72 100644
--- a/src/Runner/PoolRunner.php
+++ b/src/Runner/PoolRunner.php
@@ -38,7 +38,7 @@ public function loop(Pool $pool): void
         $futures = [];
 
         while (!$pool->isEmpty()) {
-            $test = $pool->getTestToRun();
+            $test = $pool->getNextTestToRun();
 
             if (null === $test) {
                 Future\awaitAny($futures);
diff --git a/src/Runner/TestStorage.php b/src/Runner/TestStorage.php
index 2ad275a..12d6a4a 100644
--- a/src/Runner/TestStorage.php
+++ b/src/Runner/TestStorage.php
@@ -7,6 +7,7 @@
 /** @internal */
 final class TestStorage
 {
+    /** @var \WeakMap<\Fiber<void, void, void, void>, Test|null>|null */
     private static ?\WeakMap $localStorage = null;
 
     public static function set(Test $test): void
@@ -17,7 +18,9 @@ public static function set(Test $test): void
             return;
         }
 
+        /* @phpstan-ignore-next-line */
         self::$localStorage ??= new \WeakMap();
+        /* @phpstan-ignore-next-line */
         self::$localStorage[$fiber] = $test;
     }
 
@@ -29,8 +32,10 @@ public static function get(): ?Test
             return null;
         }
 
+        /* @phpstan-ignore-next-line */
         self::$localStorage ??= new \WeakMap();
 
+        /* @phpstan-ignore-next-line */
         return self::$localStorage[$fiber] ?? null;
     }
 }
diff --git a/src/Test.php b/src/Test.php
index 136a64b..8475406 100644
--- a/src/Test.php
+++ b/src/Test.php
@@ -2,7 +2,10 @@
 
 namespace Asynit;
 
-class Test
+/**
+ * @internal
+ */
+final class Test
 {
     public const STATE_PENDING = 'pending';
     public const STATE_RUNNING = 'running';
@@ -13,7 +16,7 @@ class Test
     /** @var Test[] */
     private array $parents = [];
 
-    /** @var Test[] */
+    /** @var array<array{ test: Test, skipIfFailed: bool }> */
     private array $children = [];
 
     /** @var mixed[] */
diff --git a/src/TestSuite.php b/src/TestSuite.php
new file mode 100644
index 0000000..c24449e
--- /dev/null
+++ b/src/TestSuite.php
@@ -0,0 +1,22 @@
+<?php
+
+namespace Asynit;
+
+/**
+ * @internal
+ *
+ * @template T of object
+ */
+final class TestSuite
+{
+    /** @var array<string, Test> */
+    public array $tests = [];
+
+    /**
+     * @param \ReflectionClass<T> $reflectionClass
+     */
+    public function __construct(
+        public readonly \ReflectionClass $reflectionClass
+    ) {
+    }
+}
diff --git a/src/TestWorkflow.php b/src/TestWorkflow.php
index df7e11d..01f2790 100644
--- a/src/TestWorkflow.php
+++ b/src/TestWorkflow.php
@@ -4,7 +4,10 @@
 
 use Asynit\Output\OutputInterface;
 
-class TestWorkflow
+/**
+ * @internal
+ */
+final class TestWorkflow
 {
     public function __construct(private OutputInterface $output)
     {
@@ -21,7 +24,7 @@ public function markTestAsRunning(Test $test): void
         $debugOutput = ob_get_contents();
         ob_clean();
 
-        $this->output->outputStep($test, $debugOutput);
+        $this->output->outputStep($test, false === $debugOutput ? '' : $debugOutput);
     }
 
     public function markTestAsSuccess(Test $test): void
@@ -34,7 +37,7 @@ public function markTestAsSuccess(Test $test): void
 
         $debugOutput = ob_get_contents();
         ob_clean();
-        $this->output->outputSuccess($test, $debugOutput);
+        $this->output->outputSuccess($test, false === $debugOutput ? '' : $debugOutput);
     }
 
     public function markTestAsFailed(Test $test, \Throwable $error): void
@@ -71,6 +74,6 @@ public function markTestAsSkipped(Test $test): void
 
         $debugOutput = ob_get_contents();
         ob_clean();
-        $this->output->outputSkipped($test, $debugOutput);
+        $this->output->outputSkipped($test, false === $debugOutput ? '' : $debugOutput);
     }
 }