[9.x] Add assertUnsupportedMediaType method for assertion Unsupported…

… Media Type (#46418)

Co-authored-by: Shamimul Alam <bd.shawon1991@gmail.com>

src/Illuminate/Testing/Concerns/AssertsStatusCodes.php

@@ -143,6 +143,16 @@ public function assertConflict()
         return $this->assertStatus(409);
     }
 
+    /**
+     * Assert that the response has a 415 "Unsupported Media Type" status code.
+     *
+     * @return $this
+     */
+    public function assertUnsupportedMediaType()
+    {
+        return $this->assertStatus(415);
+    }
+
     /**
      * Assert that the response has a 422 "Unprocessable Entity" status code.
      *