added readme file about diagnostic tests directives

compiler/testData/diagnostics/ReadMe.md

@@ -0,0 +1,44 @@
+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:
+
+    class _<T>
+    fun <T> T.checkType(f: (_<T>) -> Unit) = f
+
+With that, an exact type of an expression can be checked in the following way:
+
+    fun test(expr: A) {
+       expr checkType { it: _<A> }
+    }
+
+#### Usage:
+
+    // !CHECK_TYPE

compiler/tests/org/jetbrains/jet/checkers/BaseDiagnosticsTest.java

@@ -150,7 +150,7 @@ public abstract class BaseDiagnosticsTest extends JetLiteFixture {
                         "where '+' means 'include'\n" +
                         "      '-' means 'exclude'\n" +
                         "      '!' means 'exclude everything but this'\n" +
-                        "directives are applied in the order of appearance, i.e. !FOO +BAR means inluce only FOO and BAR");
+                        "directives are applied in the order of appearance, i.e. !FOO +BAR means include only FOO and BAR");
         }
         boolean first = true;
         do {