Add tests for unused-features

Author: mu001999

tests/ui/lint/unused-features/allow-unused-features.rs

@@ -0,0 +1,6 @@
+//@ check-pass
+
+#![crate_type = "lib"]
+#![allow(unused_features)]
+
+#![feature(unboxed_closures)]

tests/ui/lint/unused-features/deny-unused-features.rs

@@ -0,0 +1,4 @@
+#![crate_type = "lib"]
+#![deny(unused_features)]
+
+#![feature(unboxed_closures)] //~ ERROR feature `unboxed_closures` is declared but not used

tests/ui/lint/unused-features/deny-unused-features.stderr

@@ -0,0 +1,14 @@
+error: feature `unboxed_closures` is declared but not used
+  --> $DIR/deny-unused-features.rs:4:12
+   |
+LL | #![feature(unboxed_closures)]
+   |            ^^^^^^^^^^^^^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/deny-unused-features.rs:2:9
+   |
+LL | #![deny(unused_features)]
+   |         ^^^^^^^^^^^^^^^
+
+error: aborting due to 1 previous error
+