Move /src/test to /tests

tests/ui/async-await/async-borrowck-escaping-closure-error.rs

@@ -0,0 +1,10 @@
+// edition:2018
+#![feature(async_closure)]
+fn foo() -> Box<dyn std::future::Future<Output = u32>> {
+    let x = 0u32;
+    Box::new((async || x)())
+    //~^ ERROR E0373
+}
+
+fn main() {
+}