[SOLVED] Windows PowerShell 5.1 cannot import local module file with `using module` but Pwsh 7 can

Windows PowerShell 5.1 cannot import local module file with `using module` but Pwsh 7 can

I have the following directory structure:

└─ScriptModuleRepositoryTemplate
  │   ScriptModuleRepositoryTemplate.psd1
  │   ScriptModuleRepositoryTemplate.psm1
  │   ScriptModuleRepositoryTemplate.Tests.ps1

At the top of the Pester ScriptModuleRepositoryTemplate.Tests.ps1 file I have this statement to import the module:

using module './ScriptModuleRepositoryTemplate.psm1'

The module is imported and the Pester tests run fine in Pwsh 7, but on Windows PowerShell 5.1 it throws the error:

System.IO.FileNotFoundException: The specified module 'D:\a\PowerShell.ScriptModuleRepositoryTemplate\PowerShell.ScriptModuleRepositoryTemplate\ScriptModuleRepositoryTemplate.psm1' was not loaded because no valid module file was found in any module directory.

If I instead use Import-Module like this:

Import-Module -Name "$PSScriptRoot/ScriptModuleRepositoryTemplate.psm1"

it works in both PowerShell 5.1 and 7, but of course Import-Module does not import classes and enums, so I need to use using module.

Both Pwsh and Windows PowerShell are using Pester v5.5.0, so I don't think the issue is with Pester, but with Windows PowerShell itself.

I can reproduce the issue on my local machine by running Invoke-Pester ., as well as in GitHub Actions (see this workflow run in the open source project).

Does anyone have any ideas on how I can get using module './PathToModuleFile.psm1' to work properly?

Solution

Ugggghh, it turns out the problem was using the forward slash / in the module file path 🤦‍♂️. It seems the forward slash works fine with Import-Module in Windows PowerShell, but not with using module.

Once I changed:

using module './ScriptModuleRepositoryTemplate.psm1'

to:

using module '.\ScriptModuleRepositoryTemplate.psm1'

then it worked fine in Windows PowerShell 5.1 and Pwsh 7.