Merge pull request #321 from Lukasss93/abstracts-modifier

[4.x] Add `abstracts()` modifier to architectural testing documentation

Author: nunomaduro

arch-testing.md

@@ -735,6 +735,7 @@ Sometimes, you may want to apply the given expectation but excluding certain typ
 - [`extending()`](#modifier-extending)
 - [`implementing()`](#modifier-implementing)
 - [`using()`](#modifier-using)
+- [`abstracts()`](#modifier-abstracts)
 
 </div>
 
@@ -851,6 +852,18 @@ arch('app')
     ->using(HasFactory::class)
     ->toExtend(Model::class);
 ```
+
+<a name="modifier-abstracts"></a>
+### `abstracts()`
+
+The `abstracts()` modifier allows you to restrict the expectation to only abstract classes.
+
+```php
+arch('app')
+    ->expect('App')
+    ->abstracts()
+    ->toImplement(JsonSerializable::class);
+```
 ---
 
 In this section, you have learned how to perform architectural testing, ensuring that your application or library's architecture meets a specified set of architectural requirements. Next, have you ever wondered how to test the performance of your code? Let's explore [Stress Testing](/docs/stress-testing).