message: Test CACHEDIR.TAG is created in an existing registry
diff: @@ -1237,6 +1237,12 @@ fn updating_a_dep(cargo: fn(&Project, &str) -> Execs) {
  .run();
  assert!(paths::home().join(".cargo/registry/CACHEDIR.TAG").is_file());
  + // Now delete the CACHEDIR.TAG file: this is the situation we'll be in after
  + // upgrading from a version of Cargo that doesn't mark this directory, to one that
  + // does. It should be recreated.
  + fs::remove_file(paths::home().join(".cargo/registry/CACHEDIR.TAG"))
  + .expect("remove CACHEDIR.TAG");
  +
  p.change_file(
  "a/Cargo.toml",
  r#"
  @@ -1265,6 +1271,11 @@ fn updating_a_dep(cargo: fn(&Project, &str) -> Execs) {
  ",
  )
  .run();
  +
  + assert!(
  + paths::home().join(".cargo/registry/CACHEDIR.TAG").is_file(),
  + "CACHEDIR.TAG recreated in existing registry"
  + );
  }
  #[cargo_test]
  