add test for #28134

Author: euclio

src/test/ui/issues/issue-28134.rs

@@ -0,0 +1,13 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// compile-flags: --test
+
+#![test] //~ ERROR only functions may be used as tests

src/test/ui/issues/issue-28134.stderr

@@ -0,0 +1,8 @@
+error: only functions may be used as tests
+  --> $DIR/issue-28134.rs:13:1
+   |
+LL | #![test] //~ ERROR only functions may be used as tests
+   | ^^^^^^^^
+
+error: aborting due to previous error
+