I think test modules should use the namespace: Microsoft.PowerShell.Test.*

I discussed this with Amber and her view was that we may be better off changing this when we move to NuGet gallery or reach the situation when we need the names to have the Microsoft namespace to stand out and not conflict with generic test modules. The way to change the name from something like test_module to Microsoft.PowerShell.Test.* is to either create a new module with this name or to update it in the database/from the backend which Amber could do. It's not a simple update by publishing the module with an updated version (with the name change made in). So her suggestion was to update once when we know for sure what we want it to be like.

these file paths only work on Windows and only if that machine has C: drive which isn't guaranteed

Good point! My thought was that this filepath gets changed before it's ever used, but I see that it's better to not have to rely on that alone. Better to not introduce something that could cause an issue later or if misused. Additionally, this really helped my understanding of how PSGet registers the default repos and which ones. I removed this and instead register the test repo and unregister it in the PSGetTestUtils file now, with Join-Path to create the path.

Why is -ErrorAction Ignore used here?

Is there a reason to filter out incorrect results that may be returned? Seems like this test should validate that each returned module has the right name

I thought we were going to use namespaced test module names?

This code is similar in several cases, you can use -TestCases with splatting to cover different parameter variations and use the same validation code. Something like:

It "... with parameter '<Parameter>'" -TestCases @(
  @{ Parameter = 'Name' }
  @{ Parameter = 'ModuleName' }
) {
  param($parameter)
  ...
  $parameters = @{
    $parameter = 'test_module'
    Version = '*'
    Repository = $TestGalleryName
  }

  Find-PSResource @parameters

lots of repetition, so recommend storing repeated values in a variable in case they need to change in the future or reused

stored in variable.