Several directives can be added in the beginning of a test file in the syntax:

`// !DIRECTIVE`

## Directives:

### 1. DIAGNOSTICS

Must be

    '([ + - ! ] DIAGNOSTIC_FACTORY_NAME | ERROR | WARNING | INFO ) +'

  where

* `+` means 'include';
* `-` means 'exclude';
* `!` means 'exclude everything but this'.

  Directives are applied in the order of appearance, i.e. `!FOO +BAR` means include only `FOO` and `BAR`.

#### Examples:

    // !DIAGNOSTICS: -WARNING +CAST_NEVER_SUCCEEDS

    // !DIAGNOSTICS: -UNUSED_EXPRESSION -UNUSED_PARAMETER -UNUSED_VARIABLE


### 2. CHECK_TYPE

The directive adds the following declarations to the file:

    fun <T> checkSubtype(t: T) = t

    class Inv<T>
    fun <E> Inv<E>._() {}
    infix fun <T> T.checkType(f: Inv<T>.() -> Unit) {}

With that, an exact type of an expression can be checked in the following way:

    fun test(expr: A) {
       expr checkType { _<A>() }
    }

#### Usage:

    // !CHECK_TYPE

### 3. FILE

The directive lets you compose a test consisting of several files in one actual file.

#### Usage:

    // FILE: A.java
    /* Java code */

    // FILE: B.kt
    /* Kotlin code */

### 4. LANGUAGE

This directive lets you enable or disable certain language features. Language features are named as
enum entries of the class LanguageFeature. Each feature can be enabled with `+` or disabled with `-`.

#### Usage:

    // !LANGUAGE: -TopLevelSealedInheritance

    // !LANGUAGE: +TypeAliases -LocalDelegatedProperties