Use (Spock Framework API Documentation (2.3))

```
@Retention(RUNTIME)
@Target({TYPE,METHOD})
@Repeatable(Container.class)
public @interface Use
```
Activates one or more Groovy categories while the annotated spec method or class executes. In other words, @Use(SomeCategory) has the same effect as wrapping the execution of the annotated method or class with use(SomeCategory) { ... }.
Basic example:
```
 class ListExtensions {
   static avg(List list) { list.sum() / list.size() }
 }

 class MySpec extends Specification {
   @Use(ListExtensions)
   def "can use avg() method"() {
     expect:
     [1, 2, 3].avg() == 2
   }
 }
 
```
One use case for this feature is the stubbing of dynamic methods which are usually provided by the runtime environment (e.g. Grails).
Note: @Use has no effect when applied to a helper method. However, when applied to a spec class it will also affect its helper methods.
Note: If this extension is applied on the Specification, then it will use ExecutionMode.SAME_THREAD for the whole Spec.

- Required Element Summary
  
  Required Elements
  Modifier and Type Required Element Description
  
  Class[] value

- Element Detail
  - value
```
Class[] value
```