Document #[test_case] and #![test_runner]

src/test/ui/issues/issue-11692-2.rs

@@ -10,5 +10,5 @@
 
 fn main() {
     concat!(test!());
-    //~^ error: `test` can only be used in attributes
+    //~^ error: cannot find macro `test!` in this scope
 }

src/test/ui/issues/issue-11692-2.stderr

@@ -1,4 +1,4 @@
-error: `test` can only be used in attributes
+error: cannot find macro `test!` in this scope
   --> $DIR/issue-11692-2.rs:12:13
    |
 LL |     concat!(test!());

src/test/ui/test-shadowing/auxiliary/test_macro.rs

@@ -11,4 +11,4 @@
 #[macro_export]
 macro_rules! test {
     () => {};
-}
+}

src/test/ui/test-shadowing/test-cant-be-shadowed.rs

@@ -15,4 +15,4 @@
 #[macro_use] extern crate test_macro;
 
 #[test]
-fn foo(){}
+fn foo(){}