How to create a wrapper for an advanced function cmdlet that uses dynamic parameters

Question

I'm trying to create a wrapper (proxy) for Pester's Should cmdlet. Possible use cases include transparent logging of test input even in case of success and improve the way Pester logs objects of certain types, e. g. hashtable.

As Should is an advanced function, forwarding arguments via $args splatting does not work.

So I tried to generate a wrapper using System.Management.Automation.ProxyCommand::Create(), as described by this answer:

$cmd = Get-Command Should
$wrapperSource = [System.Management.Automation.ProxyCommand]::Create( $cmd )
$wrapperSource >should_wrapper.ps1

When calling the wrapper, Powershell outputs this error message:

Should: Parameter set cannot be resolved using the specified named parameters. One or more parameters issued cannot be used together or an insufficient number of parameters were provided.

It looks like the wrapper generator doesn't understand the dynamicparam declaration of Should.

How to write a generic wrapper for Pester's Should without duplicating Pester code?

Xmas

Answer 1

It looks like the wrapper generator doesn't understand the dynamicparam declaration of Should.

The wrapper generator omits dynamicparam by default. Fortunately, this is easily fixed with a bit of templating:

$cmd = Get-Command Should
$pct = [System.Management.Automation.ProxyCommand]
$wrapperSource = @(
  $pct::GetCmdletBindingAttribute($cmd)
  'param('
    $pct::GetParamBlock($cmd)
  ')'
  'dynamicparam {'
    $pct::GetDynamicParam($cmd)
  '}'
  'begin {'
    $pct::GetBegin($cmd)
  '}'
  'process {'
    $pct::GetProcess($cmd)
  '}'
  'end {'
    $pct::GetEnd($cmd)
  '}'
) -join [Environment]::NewLine

Azote

There is a typo, it should be param ( ... ). After fixing that, when calling the wrapper like 0 | .\shouldWrapper.ps1 -Be 1 I get this error message: "Should: Parameter set cannot be resolved using the specified named parameters. One or more parameters issued cannot be used together or an insufficient number of parameters were provided." – Xmas

Odd. What version of Pester are you using? It works for me with Pester 3.4 in Windows PowerShell 5.1 and with Pester 5 on PowerShell 7.1 – Azote

It failed with Pester 5.0.4 but works with Pester 5.1.1 on both PS versions. – Xmas

There is an overload of ProxyCommand.Create() that has a boolean parameter generateDynamicParameters, but doesn't appear to have any effect. Possibly a bug? – Xmas

That's my impression, I've never gotten that overload to work - hence the stichwork above :-) – Azote

Nicely done. It is indeed a bug, and it's worth noting that it only affects (advanced) functions and scripts, not compiled cmdlets - see GitHub issue #4792; I've added a comment there to point to the workaround here. /cc @Xmas – Presence

@zett42, you're right, the bug is still there, and the report should not have been closed. I've left a comment to that effect, with a simpler repro (the original repro was a bit unclear). – Presence