Add tests for multiple underscore and non-underscore lifetimes

src/test/compile-fail/underscore-lifetime-binders.rs

@@ -25,6 +25,8 @@ fn meh() -> Box<for<'_> Meh<'_>> //~ ERROR invalid lifetime parameter name: `'_`
   Box::new(5u8)
 }
 
+fn foo2(_: &'_ u8, y: &'_ u8) -> &'_ u8 { y } //~ ERROR missing lifetime specifier
+
 fn main() {
     let x = 5;
     foo(Foo(&x));

src/test/compile-fail/underscore-lifetime-elison-mismatch.rs

@@ -0,0 +1,15 @@
+// Copyright 2017 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.
+
+#![feature(underscore_lifetimes)]
+
+fn foo(x: &mut Vec<&'_ u8>, y: &'_ u8) { x.push(y); } //~ ERROR lifetime mismatch
+
+fn main() {}