Bunching expensive setup in Pester

discover-setup-run.ps1

## Run only discovery, select tests that need really expensive setup that takes 
# long time to be present in the target system. E.g. 30 minutes per file to be updated
# in a remote resource. And run just the discovery, setup all tests that would run across
# all files (we use only one here but it does not matter). 
# And then run the tests, communicating back which resources were created so we get failures
# in their respective tests. 

Import-Module Pester -RequiredVersion 5.2.0 -Force 

$configuration = [PesterConfiguration]::Default 
$configuration.Run.Container = New-PesterContainer -Path $PSScriptRoot
$configuration.Run.SkipRun = $true 
$configuration.Run.PassThru = $true
$configuration.Filter.ExcludeTag = "Excluded"
$configuration.Output.Verbosity = "Detailed"

# run only discovery because $configuration.Run.SkipRun = $true 
$discovered = Invoke-Pester -Configuration $configuration

# get tests that need setup and are specifying the required group name in their data
# you should see two, the last one is excluded by filter
$testsThatNeedSetup = $discovered.Tests | 
    Where-Object { $_.ShouldRun -and $_.Data -is [Hashtable] -and $_.Data.ContainsKey("RequiredGroupName") }

# setup groups
# wait till the are done, and collect them in array as they come
$groups = "Group1", "Group12"

# enable the run again
$configuration.Run.SkipRun = $false
$configuration.Run.Container.Value[0].Data = @{ Groups = $groups }

$result = Invoke-Pester -Configuration $configuration

validate.Tests.ps1

# don't make this mandatory, you will provide it only when you run, but not for the 
# discovery only part
param ($Groups)

Describe "A" { 
    BeforeEach  { 
        # in your helper module probably
        function Assert-GroupExist ($Group, $RequiredGroupName) { 
            # whatever you need to do to ensure you have it created either by querying the resource or
            # by loooking into the hashtable your provided
            if ($RequiredGroupName -notin $Group) { 
                throw "Group $RequiredGroupName is required but it was not created."
            }
        }

        # $RequiredGroupName comes from Foreach on the test
        Assert-GroupExist -Group $Groups -RequiredGroupName $RequiredGroupName
    }

    It "Tests <RequiredGroupName>" -ForEach @{ RequiredGroupName = "Group1" } {
        
    }

    It "Tests <RequiredGroupName>" -ForEach @{ RequiredGroupName = "Group2" } {
        
    }

    It "Tests <RequiredGroupName>" -ForEach @{ RequiredGroupName = "Group3" } -Tag "Excluded" {
        
    }
}