add test runtime macro (#2409)

tests/test-macro-import-conflict.rs

@@ -0,0 +1,15 @@
+//! Checks that test macro does not cause problems in the presence of imports named "test" that
+//! could be either a module with test items or the "test with runtime" macro itself.
+//!
+//! Before actix/actix-net#399 was implemented, this macro was running twice. The first run output
+//! `#[test]` and it got run again and since it was in scope.
+//!
+//! Prevented by using the fully-qualified test marker (`#[::core::prelude::v1::test]`).
+
+use actix_web::test;
+
+#[actix_web::test]
+async fn test_macro_naming_conflict() {
+    let _req = test::TestRequest::default();
+    assert_eq!(async { 1 }.await, 1);
+}