diff --git a/composer.json b/composer.json
index e218cbd..805a8ed 100644
--- a/composer.json
+++ b/composer.json
@@ -66,7 +66,12 @@
     "scripts": {
         "fix-lint": "phpcbf --standard=ZEND --standard=PSR2 --ignore=*/vendor/* ./",
         "lint": "phpcs --standard=ZEND --standard=PSR2 --ignore=*/vendor/* ./",
-        "test": "phpunit tests",
+        "test": [
+            "@test-unit",
+            "@test-integration"
+        ],
+        "test-unit": "phpunit tests/Unit",
+        "test-integration": "phpunit tests/Integration",
         "static-check": "phpstan analyse src --level 8"
     },
     "suggest": {
diff --git a/src/Zipkin/Instrumentation/Http/Request.php b/src/Zipkin/Instrumentation/Http/Request.php
index 193ea10..8dc665c 100644
--- a/src/Zipkin/Instrumentation/Http/Request.php
+++ b/src/Zipkin/Instrumentation/Http/Request.php
@@ -60,7 +60,7 @@ abstract public function getUrl(): string;
     abstract public function getHeader(string $name): ?string;
 
     /**
-     * @return object|null the underlying request object or {@code null} if there is none.
+     * @return mixed the underlying request object or {@code null} if there is none.
      */
-    abstract public function unwrap(): ?object;
+    abstract public function unwrap();
 }
diff --git a/src/Zipkin/Instrumentation/Http/Response.php b/src/Zipkin/Instrumentation/Http/Response.php
index 90fcd6a..e1034fd 100644
--- a/src/Zipkin/Instrumentation/Http/Response.php
+++ b/src/Zipkin/Instrumentation/Http/Response.php
@@ -27,7 +27,7 @@ abstract public function getRequest();
     abstract public function getStatusCode(): int;
 
     /**
-     * @return object|null the underlying response object or {@code null} if there is none.
+     * @return mixed the underlying response object or {@code null} if there is none.
      */
-    abstract public function unwrap(): ?object;
+    abstract public function unwrap();
 }