move_ref_patterns: introduce tests

bindings_after_at: harden tests

src/test/ui/pattern/move-ref-patterns/move-ref-patterns-default-binding-modes.rs

@@ -0,0 +1,16 @@
+#![feature(move_ref_pattern)]
+
+fn main() {
+    struct U;
+
+    // A tuple is a "non-reference pattern".
+    // A `mut` binding pattern resets the binding mode to by-value.
+
+    let p = (U, U);
+    let (a, mut b) = &p;
+    //~^ ERROR cannot move out of a shared reference
+
+    let mut p = (U, U);
+    let (a, mut b) = &mut p;
+    //~^ ERROR cannot move out of a mutable reference
+}