Introduce NotImplementedError instead of UnsupportedOperationException to throw from TODO function.

#KT-8153

libraries/stdlib/src/kotlin/util/Standard.kt

@@ -1,17 +1,21 @@
 package kotlin
 
-
 /**
- * Always throws an [UnsupportedOperationException] stating that operation is not implemented.
+ * An exception is thrown to indicate that a method body remains to be implemented.
  */
-public fun TODO(): Nothing = throw UnsupportedOperationException("An operation is not implemented.")
+public class NotImplementedError(message: String = "An operation is not implemented.") : Error(message)
 
 /**
- * Always throws an [UnsupportedOperationException] stating that operation is not implemented.
+ * Always throws [NotImplementedError] stating that operation is not implemented.
+ */
+public fun TODO(): Nothing = throw NotImplementedError()
+
+/**
+ * Always throws [NotImplementedError] stating that operation is not implemented.
  *
  * @param reason a string explaining why the implementation is missing.
  */
-public fun TODO(reason: String): Nothing = throw UnsupportedOperationException("An operation is not implemented: $reason")
+public fun TODO(reason: String): Nothing = throw NotImplementedError("An operation is not implemented: $reason")
 
 
 /**

libraries/stdlib/test/utils/TODOTest.kt

@@ -27,12 +27,12 @@ private class PartiallyImplementedClass {
 
 class TODOTest {
     private fun assertNotImplemented(block: () -> Unit) {
-        assertTrue(fails(block) is UnsupportedOperationException)
+        assertTrue(fails(block) is NotImplementedError)
     }
 
     private fun assertNotImplementedWithMessage(message: String, block: () -> Unit) {
         val e = fails(block)
-        assertTrue(e is UnsupportedOperationException)
+        assertTrue(e is NotImplementedError)
         assertTrue(message in e!!.getMessage()!!)
     }