localappdata-test-isolation

name	localappdata-test-isolation
description	Isolate tests for services that write under %LOCALAPPDATA% without touching the real user profile.
domain	testing
confidence	high
source	earned

Context

Use this skill when a unit test exercises code that writes beneath %LOCALAPPDATA%, such as %LOCALAPPDATA%\CopilotBooster\models-cache.json.

Patterns

• Create a unique temp directory per test instance.
• Save the original LOCALAPPDATA environment value.
• Set LOCALAPPDATA before constructing the service under test.
• Restore the original environment value in Dispose or finally.
• Delete the temp tree during cleanup.
• Production code should resolve Environment.GetEnvironmentVariable("LOCALAPPDATA") first, then fall back to Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData), so tests can redirect the location deterministically.

Examples

tests\Services\CopilotModelsServiceTests.cs uses a per-test temp %LOCALAPPDATA% root and writes/reads CopilotBooster\models-cache.json there.

Anti-Patterns

• Do not write tests against the real user %LOCALAPPDATA% folder.
• Do not assume Environment.GetFolderPath(SpecialFolder.LocalApplicationData) honors process-level LOCALAPPDATA changes on Windows.
• Do not leave global environment variables modified after a test.