proposal: testing: add more support to automatically cleanup temporary resources or temporary changes to the global environment

[perillo]

In go 1.15, the testing package supports the T.TempDir function.
Currently the method is not used in the tests of the go distribution, but os.MkdirTemp is used 164 times.

Here is a list of additional API to manage temporary resources or temporary changes to the global environment in tests:

• T.ChTempDir
  Currently all: tests that change the working directory should use defer to restore it #45182 has introduced the chdir function, but there are several tests that use it.
  os.Chdir is used 53 times (including in chdir and chtmpdir), the new chdir is used 8 times and the old chtmpdir is used 22 times.

• T.TempFile.
  Currently os.CreateTemp is used 33 times in tests.

• T.SetTempEnv
  Currently os.Setenv is used 108 times.

The usage number has been computed with a simple: grep -F "fname(" **/*_test.go | wc -l

[dmitshur]

CC @mpvl via owners.

[perillo]

As an alternative these functions can be added to an internal package. In #45182 I have proposed internal/ostest.

Thanks.

[perillo]

I noted only now that Setenv was already added to the testing package a month ago.

Is it possible to send now changes to use the new API or it is better to wait after go 1.17 has been released?

[dmitshur]

Most API additions to the testing package would likely need to go through the proposal process and get approved before being added. It is better to wait until the proposal is approved before sending CLs, unless you need to prototype the changes in order to inform the proposal itself.

[perillo]

Yes, but as I wrote T.Setenv has already be added a month ago. However I don't know if it is still possible to remove it before the freeze for Go 1.17.

[dmitshur]

Adding TB.Setenv was an accepted proposal #41260.

[rsc]

Now that t.Setenv exists, it is OK to send CLs to the Go repo to use t.Setenv if that cleans up a test.
We can always rollback those CLs with the rollback of Setenv if that happens (seems unlikely).

[rsc]

Given that Setenv and TempDir already exist, it doesn't seem like we need to add ChTempDir (that's just Chdir), nor t.TempFile (that can use os.TempFile with the t.TempDir result).

We could consider adding t.Chdir instead of t.ChTempDir, but any test that uses Chdir at all is unparallelizable. Adding t.Chdir to the API may suggest writing tests that don't scale well. I also don't understand why tests would really need to Chdir. It's almost always better to pass the directory to the function that needs it (like setting cmd.Dir in os/exec). So probably t.Chdir is below the bar, especially since you can already use t.Cleanup to un-Chdir.

[rsc]

This proposal has been added to the active column of the proposals project
and will now be reviewed at the weekly proposal review meetings.
— rsc for the proposal review group

[perillo]

@rsc I agree that functions like ChTempDir or Chdir are not suitable for the testing package. However adding them to an internal package should be fine. The problem is that that package may become something like ioutil.

As for why to chdir in a test, I'm not sure.
Some test probably do it for convenience, as an example: https://github.com/golang/go/blob/master/src/os/os_test.go#L968.
Several tests that tests symlinks seems to call Chdir.

For some other test it may necessary, as an example: https://github.com/golang/go/blob/master/src/runtime/syscall_windows_test.go#L1046

[rsc]

It sounds like the only thing left is t.Chdir and we agree it's not a good idea.
We don't even need to add it to an internal package.
Sometimes duplicated code is OK.

[perillo]

Fine with me, thanks. However if possible I would like to have all these functions in a custom, unique file, e.g. testutil_test.go, so that it easy to find them and make sure that the functions defined in multiple packages are in sync.

Currently we have chtmpdir, tempDirCanonical and I plan to add writeFile(t *testing.T, name string, data string) to make tests a bit more readable and consistent. Later some functions may be moved to testing or a shared internal package, if they are really useful.

[rsc]

Based on the discussion above, this proposal seems like a likely decline.
— rsc for the proposal review group

[rsc]

No change in consensus, so declined.
— rsc for the proposal review group