I'm trying to enable test caching between CI runs on Windows as discussed on Slack. It turned out to be a bit tricky, and it's still a work in progress. Here are some of the problems I ran into:

1. Even though the setup-go action caches the GOCACHE directory, it only does so when go.sum files change. We need to cache test results more frequently.

2. To address point 1, I leveraged actions/cache directly. However, the GOCACHE directory is about 1.5GB in size. Because Windows disks on GitHub action runners (Depot included) are notoriously slow, it takes a minute and a half to restore it. I think most of the time is spent on unarchiving.

3. A Go test is cached if none of its inputs change. A test's inputs include any environment variables it reads, files it reads from disk (if they are within the test's package directory), and code dependencies.

   • Many of our tests read the PATH variable. However, on Windows, the setup-terraform action updates the PATH variable with a directory that's a randomly generated UUID—the directory that contains the terraform binary. This means any test that reads the PATH variable will not be cached.
   • The go test runtime determines whether a file input has changed based not on the file's contents, but on its last modified timestamp (and a couple of other attributes). Git does not store these timestamps, so they are all set to the current date and time. In order for tests to be cached, these timestamps have to be normalized.

I've developed PoC solutions to address these issues, but I still have some work to do to make them ready to merge.