Aliases for dynamic parameters cannot be used in ParameterFilter blocks

[renehernandez]

1. General summary of the issue

Parameter Aliases are not properly handled for dynamic parameters in Mock

The following function and test highlight the issue:

function New-DynamicAttr($ParamDictionary, $Name, $Alias = $null) {
    $attr = New-Object -Type `
        System.Management.Automation.ParameterAttribute
    $attr.Mandatory = $false
    $attr.ParameterSetName = '__AllParameterSets'
    $attributeCollection = New-Object `
        -Type System.Collections.ObjectModel.Collection[System.Attribute]
    $attributeCollection.Add($attr)

    if ($null -ne $Alias) {
        $attr = New-Object -Type `
            System.Management.Automation.AliasAttribute -ArgumentList @($Alias)
        $attributeCollection.Add($attr)
    }

    $dynParam1 = New-Object -Type `
        System.Management.Automation.RuntimeDefinedParameter($Name, [string],
        $attributeCollection)

    $ParamDictionary.Add($Name, $dynParam1)
}

function Test-DynamicParam {
    [CmdletBinding()]
    param(
        [String]$Name
    )

    dynamicparam {
        if ($Name.StartsWith("Hello")) {
            $paramDictionary = New-Object `
                -Type System.Management.Automation.RuntimeDefinedParameterDictionary
             New-DynamicAttr -ParamDictionary $paramDictionary -Name "Path" -Alias "Location"

            return $paramDictionary
        }
    }

    process {
        if ($PSBoundParameters.Path) {
            Write-Host "PSEdition value: $($PSBoundParameters.Path)"
        }
    }
}

Describe 'Usage of Alias in DynamicParams' {
    Context 'Usage of ParameterFilters in Mock' {

       It 'using parameter alias' {
            Mock Test-DynamicParam { "World" } -ParameterFilter {$Location -eq 'Here'}

            Test-DynamicParam -Name "Hello" -Location "Here" | Should -Be 'World'
        }
    }

     Context 'Usage of ParameterFilters in Assert-MockCalled' {
        It 'using parameter alias' {
            Mock Test-DynamicParam { "World" } -ParameterFilter {$Location -eq 'Here'}

            Test-DynamicParam -Name "Hello" -Location "Here" | Should -Be 'World'

            Assert-MockCalled Test-DynamicParam -ParameterFilter {$Location -eq 'Here'}
        }
    }
}

2. Describe Your Environment

Pester version     : 4.7.3 C:\Program Files\PowerShell\Modules\Pester\4.7.3\Pester.psd1
PowerShell version : 6.1.3
OS version         : Microsoft Windows NT 10.0.17134.0

3. Expected Behavior

It should pass

4.Current Behavior

It fails

5. Possible Solution

Add corresponding implementation for dynamic parameter for what was done for regular parameters

6. Context

This is related to #1007 and #1128

[renehernandez]

@nohwnd Can you add this issue to the Better Mock milestone?

[renehernandez]

I have done some preliminary work on this and there are some nuances that we need to account for.

• Since dynamic parameters are defined at runtime, and may change between invocation, we cannot perform the detection of aliases during the mock generation phase.
• Based on this, we may have to check for aliases right before proceeding to test if a particular filter block matches, both for mock invocation (most likely in FindMatchingBlock) and asserting that them mock is called, in Assert-MockCalled.
• This may lead to extra overhead in Mock execution, so we may want to analyze whether it could be worthwhile having this running under a new flag parameter for the Mock function.

@nohwnd Any thoughts?