Update-DbaInstance - Use the temp folder of the test configuration in the tests

[andreasjordan]

Summary

Update-DbaInstance.Tests.ps1 builds its fake installer folder at a fixed C:\Temp\dbatools_Update-DbaInstance (unit tests and the skipped integration Describe). Every other test file writes below $TestConfig.Temp, which is C:\Temp on CI and a folder per test set on the lab.

With two runs on one machine the fixed path is shared: during the parallel full runs of 2026-09-19 one run created and removed the folder while the other run's environment check saw it and flagged two unrelated test files (Add-DbaDbFile, Add-DbaDbMirrorMonitor) as leaving a legacy temp folder behind.

The folder now lives in $TestConfig.Temp, like everything else. On CI that is the same C:\Temp as before.

One assertion had to follow: the -Download test expects Save-DbaKbUpdate to be called with the local temp folder, which is what the command does for a local -Path. For a network share it downloads into the share itself (Test-NetworkPath at the top of the download loop). On a lab where $TestConfig.Temp is a share, the expected folder is therefore the share, and the test now derives the expectation from the same rule. On CI nothing changes.

Test plan

• Update-DbaInstance.Tests.ps1 green on PowerShell 7 and Windows PowerShell 5.1 on the lab, where $TestConfig.Temp is a UNC path: 69 tests, 68 passed, 1 skipped.
• Before the assertion change, the same run failed exactly that one download test, with Save-DbaKbUpdate called with the share as -Path.
• No dbatools_Update-DbaInstance folder left behind, neither below $TestConfig.Temp nor in C:\Temp.

created by Claude and reviewed by Andreas Jordan

🤖 Generated with Claude Code

[potatoqualitee]

Reviewed the complete patch at this exact head, including fixture paths, download assertions, production path handling, cleanup, discussions, and CI logs exercising the affected test. No material defects found.