message: assert for non-release artifacts
diff: @@ -118,7 +118,11 @@ fn clean_release() {
  ",
  ).run();
  + p.cargo("build").run();
  +
  p.cargo("clean").arg("--release").run();
  + assert!(p.build_dir().is_dir());
  + assert!(p.build_dir().join("debug").is_dir());
  assert!(!p.build_dir().join("release").is_dir());
  }
  