message: Fix flakey test on MacOS.
  `do_not_package_if_src_was_modified` can fail if the test runs too quickly
  due to mac's filesystem time resolution.
diff: @@ -4,7 +4,7 @@ use std::io::prelude::*;
  use std::path::{Path, PathBuf};
  use git2;
  -use cargotest::{cargo_process, process, ChannelChanger};
  +use cargotest::{cargo_process, process, sleep_ms, ChannelChanger};
  use cargotest::support::{cargo_exe, execs, git, paths, project, registry, path2url};
  use cargotest::support::registry::Package;
  use flate2::read::GzDecoder;
  @@ -1440,6 +1440,13 @@ fn do_not_package_if_src_was_modified() {
  "#)
  .build();
  + if cfg!(target_os = "macos") {
  + // MacOS has 1s resolution filesystem.
  + // If src/main.rs is created within 1s of src/generated.txt, then it
  + // won't trigger the modification check.
  + sleep_ms(1000);
  + }
  +
  assert_that(
  p.cargo("package"),
  execs().with_status(101)
  