fix: add global Shutdown function; allow tests to pass on Windows regardless of temp folder state after tests

[matthewmcneely]

Description

This tortured PR allows tests to complete on Windows.

Background:

• Dgraph's pstore/walstore."Close" methods do not actually close the write ahead logs
• Go tooling's TempDir() function (which deletes the contents of the allocated folder) fails in Windows because the file handles are still active

This PR adds a Windows-specific TempDir function which tries to delete the folder, but will ultimately fail. But the tests pass.

Note: Windows users will need to manually delete folders created during testing. The folders take the form of C:\Users\<USER_NAME>\AppData\Local\Temp\modusgraph_test_*

Checklist

• Code compiles correctly and linting passes locally

[Copilot]

Pull Request Overview

This PR fixes issues with tests failing on Windows by introducing a new global Shutdown function and a Windows‑specific temporary directory helper.

• Introduces a GetTempDir function that applies extra cleanup steps on Windows.
• Replaces mg.ResetSingleton() calls with mg.Shutdown() for proper engine cleanup.
• Updates tests across multiple files to use GetTempDir for file-based URIs.

Reviewed Changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
util_test.go	Added GetTempDir and updated engine cleanup to use Shutdown.
update_test.go, query_test.go, insert_test.go, delete_test.go, client_test.go, admin_test.go	Replaced t.TempDir() with GetTempDir(t) for better Windows support.
engine.go	Introduced activeEngine tracking and Shutdown functionality; updated error messages.
unit_test/api_test.go	Removed TestUserStore, potentially impacting test coverage.
CHANGELOG.md	Updated changelog to document the new Shutdown function.

Comments suppressed due to low confidence (1)

unit_test/api_test.go:1102

• The removal of TestUserStore might reduce coverage of user store functionality. Please verify that this functionality is adequately tested elsewhere or that its removal is intentional.

func TestUserStore(t *testing.T) {

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[ryanfoxtyler]

@matthewmcneely am I understanding correctly that this avoids the test failure, but running ModusGraph on Windows could still produce unexpected results?

[matthewmcneely]

@matthewmcneely am I understanding correctly that this avoids the test failure, but running ModusGraph on Windows could still produce unexpected results?

@ryanfoxtyler
The top-level tests pass on Parallels/Windows 11 which proves at least that much is working. I also ran the example apps on Parallels without error. It's just that I have NOT put in the hundreds of "reps" on Windows as I have on OSX. Given that, and the historical problems of Badger on Windows, I suggest we put forth that it's fine for local development, but for production we'd recommend Linux.