[12.x] Add assertClientError method to http-tests

Author: shane-zeng

http-tests.md

@@ -1012,6 +1012,7 @@ Laravel's `Illuminate\Testing\TestResponse` class provides a variety of custom a
 [assertSeeInOrder](#assert-see-in-order)
 [assertSeeText](#assert-see-text)
 [assertSeeTextInOrder](#assert-see-text-in-order)
+[assertClientError](#assert-client-error)
 [assertServerError](#assert-server-error)
 [assertServiceUnavailable](#assert-service-unavailable)
 [assertSessionHas](#assert-session-has)
@@ -1623,6 +1624,15 @@ Assert that the given strings are contained in order within the response text. T
 $response->assertSeeTextInOrder(array $values, $escape = true);
 ```
 
+<a name="assert-client-error"></a>
+#### assertClientError
+
+Assert that the response has a server error (>= 400 , < 500) HTTP status code:
+
+```php
+$response->assertClientError();
+```
+
 <a name="assert-server-error"></a>
 #### assertServerError