document test, don't use grep

src/test/run-make/a-b-a-linker-guard/Makefile

@@ -1,7 +1,12 @@
 -include ../tools.mk
 
+# Test that if we build `b` against a version of `a` that has one set
+# of types, it will not run with a dylib that has a different set of
+# types.
+
 all:
 	$(RUSTC) a.rs --cfg x -C prefer-dynamic
 	$(RUSTC) b.rs -C prefer-dynamic
+	$(call RUN,b)
 	$(RUSTC) a.rs --cfg y -C prefer-dynamic
-	$(call RUN,b) 2>&1 | grep "undefined symbol"
+	$(call FAIL,b)

src/test/run-make/a-b-a-linker-guard/a.rs

@@ -1,3 +1,13 @@
+// Copyright 2014 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.
+
 #![crate_name = "a"]
 #![crate_type = "dylib"]
 

src/test/run-make/a-b-a-linker-guard/b.rs

@@ -1,3 +1,13 @@
+// Copyright 2014 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.
+
 #![crate_name = "b"]
 
 extern crate a;