Passing variables from Discovery to Run phases

[dommyzee]

I have a script that does the heavy lifting in the Discovery phase. When in the Run phase, a test needs to refer back to variables in the Discovery phase for validity. Since these phases do not share scope, I am looking for guidance on how to achieve this.

A quick example where we want to validate the integrity of a parent-child lookup:

$sb = {
   BeforeDiscovery {
      $discoveryLookups = @(
         @{Id = 1; ParentId = '1' }    # Root node
         @{Id = 2; ParentId = '1' }
         @{Id = 3; ParentId = '2' }
         @{Id = 4; ParentId = '1000' } # Invalid Parent
      )
   }

   Describe 'Check Lookups' {
      Context 'Validate entries' -ForEach $discoveryLookups {
         It 'has an ID field' {
            $_.Id | Should -Not -BeNullOrEmpty
         }

         It 'has a ParentID field' {
            $_.ParentId | Should -Not -BeNullOrEmpty
         }
      }

      ## This is the test under review
      Context 'Validate Parent Lookups' {
         It 'has a Parent ID that refers to an existing ID' -ForEach $discoveryLookups {
            $entry = $_
            $entry.ParentId | Should -BeIn $discoveryLookups.Id -Because "Parent Id ${entry.ParentId} should exist as an Id"
         }
      }
   }
}

$configuration = New-PesterConfiguration -Hashtable @{
   Output = @{ Verbosity = 'Detailed'; StackTraceVerbosity = 'None' };
   Run    = @{ Container = New-PesterContainer -ScriptBlock $sb }
}

Invoke-Pester -Configuration $configuration

In the second context block, I would need to refer to the $discoveryLookups variable directly. This is because it needs to verify the integrity within the original structure. The nature of the -ForEach would only give single records.

One approach I've taken is to create a wrapper parameter, so it can be passed directly without causing an iteration, like so:#

BeforeDiscovery {
   ...
   ### Wrap the data in a single-element array - more could be added if required.
   $wrapper = @(@{Data = $discoveryLookups})
}

Describe 'Check Lookups' {
   ... 
   ### Added $wrapper with 1 value, so it doesn't interact
   Context 'Validate Parent Lookups' -ForEach $wrapper {
      BeforeAll {
         # Store .Data at the context level
         $contextLookups = $_.Data
      }

      ### Still lookup over all the elements in the $discoveryLookups
      It 'has a Parent ID that refers to an existing ID' -ForEach $discoveryLookups {
         $entry = $_
         $entry.ParentId | Should -BeIn $contextLookups.Id -Because "Parent Id $($entry.ParentId) should relate to another Id"
      }
   }
}

Huzzah and horrah this works as expected:

Starting discovery in 1 files.
Discovery found 12 tests in 11ms.
Running tests.
Describing Check Lookups
...
 Context Validate Parent Lookups
   [+] has a Parent ID that refers to an existing ID 3ms (1ms|2ms)
   [+] has a Parent ID that refers to an existing ID 2ms (1ms|1ms)
   [+] has a Parent ID that refers to an existing ID 1ms (1ms|1ms)
   [-] has a Parent ID that refers to an existing ID 15ms (15ms|1ms)
    Expected collection @(1, 2, 3, 4) to contain '1000', because Parent Id 1000 should relate to another Id, but it was not found.
Tests completed in 319ms
Tests Passed: 11, Failed: 1, Skipped: 0, Inconclusive: 0, NotRun: 0

My question is - is this the approach to take for global variables, or is there an alternative to consider?

Many thanks!

[fflaten]

Yes. Using a wrapper dictionary through -ForEach is the recommended approach. Tips:

• You don't need the array wrapper and can provide the dictionary directly like Describe 'Check Lookups' -ForEach @{ DiscoveryLookups = $discoveryLookups }
• Dictionary keys are automatically made variables so you can avoid the BeforeAll reassigning $_.Data and just use $DiscoveryLookups in Run-phase. Using capital key/variable letter to illustrate.

The alternative is script parameters (params($MyParam = 'default data')). They're automatically included in Run as well by Pester as container (file) level Data. It's typically used for providing external data when invoking Pester - but it works with default values as well.

[dommyzee]

Thank you very much for the advice. For completeness, I adjusted the code to use the following, and worked perfectly:

BeforeDiscovery { 
   $discoveryLookups = ...
}

Describe ... {
      # ...
      Context 'Validate Parent Lookups' -Foreach @{
            DiscoveryLookups = $discoveryLookups 
         } {
         It 'has a Parent ID that refers to an existing ID' -ForEach $DiscoveryLookups {
            $_.ParentId | Should -BeIn $DiscoveryLookups.Id -Because "Parent Id $($_.ParentId) should exist as an Id"
         }
      }
}

<#
Pester v5.6.1

Starting discovery in 1 files.
Discovery found 12 tests in 92ms.
Running tests.
Describing Check Lookups
...
 Context Validate Parent Lookups
   [+] has a Parent ID that refers to an existing ID 35ms (32ms|3ms)
   [+] has a Parent ID that refers to an existing ID 2ms (1ms|1ms)
   [+] has a Parent ID that refers to an existing ID 2ms (1ms|1ms)
   [-] has a Parent ID that refers to an existing ID 11ms (10ms|1ms)
    Expected collection @(1, 2, 3, 4) to contain '1000', because Parent Id 1000 should exist as an Id, but it was not found.
Tests completed in 433ms
Tests Passed: 11, Failed: 1, Skipped: 0, Inconclusive: 0, NotRun: 0
#>