Add an async demonstration

tests/assert_macro.rs

@@ -39,4 +39,4 @@ fn list_push() {
     } else {
         panic!("Intentional")
     }
-}
+}

tests/async.rs

@@ -0,0 +1,33 @@
+use futures::future::ok;
+use futures::prelude::*;
+use qadapt::assert_no_alloc;
+use qadapt::no_alloc;
+use qadapt::QADAPT;
+
+#[global_allocator]
+static Q: QADAPT = QADAPT;
+
+#[no_alloc]
+fn async_box() -> impl Future<Item = Box<u8>, Error = ()> {
+    ok(12).and_then(|e| Ok(Box::new(e)))
+}
+
+#[test]
+fn raw_call() {
+    async_box();
+}
+
+#[test]
+fn guarded_call() {
+    assert_no_alloc!(async_box());
+}
+
+#[test]
+#[should_panic]
+fn guarded_poll() {
+    if cfg!(debug_assertions) {
+        assert_no_alloc!(async_box().poll().unwrap());
+    } else {
+        panic!("Intentional")
+    }
+}