Add a test for failure to unify type parameters

Author: Jakub Bukaj

src/test/compile-fail/type-parameter-names.rs

@@ -11,6 +11,9 @@
 // Test that we print out the names of type parameters correctly in
 // our error messages.
 
-fn foo<Foo, Bar>(x: Foo) -> Bar { x } //~ ERROR expected `Bar`, found `Foo`
+fn foo<Foo, Bar>(x: Foo) -> Bar {
+    x
+//~^ ERROR expected `Bar`, found `Foo` (expected type parameter, found a different type parameter)
+}
 
 fn main() {}