Move /src/test to /tests

tests/rustdoc-ui/macro-docs.stderr

@@ -0,0 +1,20 @@
+warning: unresolved link to `long_cat`
+  --> $DIR/macro-docs.rs:5:9
+   |
+LL |         /// A
+   |         ^^^^^
+...
+LL | m!();
+   | ---- in this macro invocation
+   |
+   = note: the link appears in this line:
+           
+           [`long_cat`] is really long
+            ^^^^^^^^^^
+   = note: no item named `long_cat` in scope
+   = help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`
+   = note: `#[warn(rustdoc::broken_intra_doc_links)]` on by default
+   = note: this warning originates in the macro `m` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+warning: 1 warning emitted
+