`Restore-TestEnvironment`: New PSModulePath in target Machine is overwritten

[johlju]

The root cause is that

1. Initialize-TestEnvironment saves the current machine environment variable PSModulePath and then updates it with the path to the built module.

DscResource.Test/source/Public/Initialize-TestEnvironment.ps1

Lines 177 to 207 in 73d6c32

	$oldPSModulePath = $env:PSModulePath
	if ($null -ne $oldPSModulePath)
	{
	$oldPSModulePathSplit = $oldPSModulePath.Split([io.path]::PathSeparator)
	}
	else
	{
	$oldPSModulePathSplit = $null
	}
	if ($oldPSModulePathSplit -ccontains $moduleParentFilePath)
	{
	# Remove the existing module path from the new PSModulePath
	$newPSModulePathSplit = $oldPSModulePathSplit | Where-Object { $_ -ne $moduleParentFilePath }
	}
	else
	{
	$newPSModulePath = $oldPSModulePath
	}
	$RequiredModulesPath = Join-Path -Path $moduleParentFilePath 'RequiredModules'
	if ($newPSModulePathSplit -cnotcontains $RequiredModulesPath)
	{
	$newPSModulePathSplit = @($RequiredModulesPath) + $newPSModulePathSplit
	}
	$newPSModulePathSplit = @($moduleParentFilePath) + $newPSModulePathSplit
	$newPSModulePath = $newPSModulePathSplit -join [io.Path]::PathSeparator
	Set-PSModulePath -Path $newPSModulePath

2. The tests run for SqlSetup and the installation sets a new path to SQLPS in machine environment variable PSModulePath.

https://github.com/dsccommunity/SqlServerDsc/blob/f9bde8a61230754c078257d115103726f749570a/tests/Integration/DSC_SqlSetup.Integration.Tests.ps1#L171-L175

DscResource.Test/source/Public/Restore-TestEnvironment.ps1

Lines 38 to 47 in 73d6c32

	if ($TestEnvironment.OldPSModulePath -ne $env:PSModulePath)
	{
	Set-PSModulePath -Path $TestEnvironment.OldPSModulePath
	if ($TestEnvironment.TestType -in ('Integration','All'))
	{
	# Restore the machine PSModulePath for integration tests.
	Set-PSModulePath -Path $TestEnvironment.OldPSModulePath -Machine
	}
	}

3. After the tests finishes the command Restore-TestEnvironment reverts the machine environment variable PSModulePath to the one saved in step 1 overwriting the new path that was set in step 2.
4. All other tests no longer finds the module SQLPS and fails.

Originally posted by @johlju in dsccommunity/SqlServerDsc#1932 (comment)

[johlju]

There is also a bug that is essentially not reverting the correct state. The variable$script:MachineOldPSModulePath is set here:

DscResource.Test/source/Public/Initialize-TestEnvironment.ps1

Lines 222 to 226 in 73d6c32

	if (!$script:MachineOldPSModulePath)
	{
	Write-Warning "This will change your Machine Environment Variable"
	$script:MachineOldPSModulePath = [System.Environment]::GetEnvironmentVariable('PSModulePath', 'Machine')
	}

Is not passed here:

DscResource.Test/source/Public/Initialize-TestEnvironment.ps1

Lines 296 to 305 in 73d6c32

	# Return the test environment
	return @{
	DSCModuleName = $Module
	Module = $ModuleUnderTest
	DSCResourceName = $DscResourceName
	TestType = $TestType
	ImportedModulePath = $moduleToImportFilePath
	OldPSModulePath = $oldPSModulePath
	OldExecutionPolicy = $oldExecutionPolicy
	}

So it is never used here:

DscResource.Test/source/Public/Restore-TestEnvironment.ps1

Lines 42 to 46 in 73d6c32

	if ($TestEnvironment.TestType -in ('Integration','All'))
	{
	# Restore the machine PSModulePath for integration tests.
	Set-PSModulePath -Path $TestEnvironment.OldPSModulePath -Machine
	}

[johlju]

Before reverting the PSModulePath in the machine state it should first look if there have been new paths added to the machine state (other than the built module path) and make sure to keep them after reverting to previous state.

[johlju]

We could add this functionality behind an optional parameter KeepNewMachinePSModulePaths to avoid a breaking change. It could be integration tests that actually sets paths that must be reverted.