Unable to Mock New-Object

[tysonjhayes]

In my code I'm trying to mock a call to New-Object. I'm wondering if this is similar to #296

The relevant chunk of the code is as follows:

$shell = New-Object -ComObject 'Shell.Application'
$zip = $shell.NameSpace($zipFile)

All attempts to mock this code have been unsuccessful. Most of the time it acts as if I haven't actually called new object which results in $shell being null.

I've attempted to mock the functioning as such:

    $zipMock = New-Module -AsCustomObject -ScriptBlock {
        function NameSpace {
            New-Module -AsCustomObject -ScriptBlock {
                function Items {
                    return @{Name = 'TextFile.txt'}
                }
            }
        }
        Export-ModuleMember -Variable * -Function *
    }
    Mock New-Object -ModuleName ExamineContentZip -ParameterFilter {$ComObject -eq 'Shell.Application'} -MockWith {$zipMock}
    Mock New-Object -ModuleName ExamineContentZip -MockWith {$zipMock}
    function New-Object {return $zipMock}

This was done over three separate attempts each attempting a different mock or the finally the function. What's strange is that if I break into the function before calling $shell I can manually paste in the Mock code and it'll work. This only appears to fail if I'm calling it from the test.

[dlwyatt]

Haven't been able to reproduce this yet. I can't see your calling code in the ExamineContentZip module, but this attempt to reproduce the problem worked fine for me:

Describe 'Mocking Test' {
    $zipMock = New-Module -AsCustomObject -ScriptBlock {
        function Namespace {
            New-Module -AsCustomObject -ScriptBlock {
                function Items {
                    return @{Name = 'TextFile.txt'}
                }
            }
        }
        Export-ModuleMember -Variable * -Function *
    }

    Mock New-Object { return $zipMock } -ParameterFilter { $ComObject -eq 'Shell.Application' }

    It 'Calls the mock' {
        New-Object -ComObject Shell.Application | Should Be $zipMock
    }
}

[tysonjhayes]

Module basically contains this:

function functiontotest
{
    param
    (
        [Parameter(Mandatory=$true)]
        [ValidateNotNullOrEmpty()]
        [string] $ZipFile
    )
    $shell = New-Object -ComObject 'Shell.Application'
    $breakvar = $true;
    $zip = $shell.NameSpace($zipFile)

    foreach($item in $zip.items())
    {
        if ($item.Name -eq "TextFile.txt")
        {
            return
        }
    }

        throw "zip does not have TextFile.txt present.";
}

Test is this:

Remove-Module [e]xamineContentZip -Force
$filePath = Join-Path -Path $PSScriptRoot -Child 'ExamineContentZip.psm1'
Import-Module -Name $filePath -DisableNameChecking -ErrorAction Stop

Describe 'functiontotest' {
    Context 'Should return null if TextFile is present' {
        $zipMock = New-Module -AsCustomObject -ScriptBlock {
            function NameSpace {
                New-Module -AsCustomObject -ScriptBlock {
                    function Items {
                        return @{Name = 'TextFile.txt'}
                    }
                }
            }
            Export-ModuleMember -Variable * -Function *
        }

        Mock New-Object { return $zipMock } -ParameterFilter { $ComObject -eq 'Shell.Application' } -ModuleName ExamineContentZip

        $expected = $null;
        $returned = functiontotest -ZipFile 'Test'

        It 'Should return null' {
            $returned | should be $expected
        }
    }
}

Right now when I remove the ModuleName flag I do not see the New-Object call mocked at all.

Mock New-Object { return $zipMock } -ParameterFilter { $ComObject -eq 'Shell.Application' }

Result:

   63:      $shell = New-Object -ComObject 'Shell.Application'
   64:*     $breakvar = $true;
   65:      $zip = $shell.NameSpace($zipFile)

[12:51:40 PM] [0008] » $shell

Application                                                 Parent
-----------                                                 ------
System.__ComObject                                          System.__ComObject

[12:51:42 PM] [0009] » $shell | gm
   TypeName: System.__ComObject#{286e6f1b-7113-4355-9562-96b7e9d64c54}

Name                 MemberType Definition
----                 ---------- ----------
AddToRecent          Method     void AddToRecent (Variant, string)
BrowseForFolder      Method     Folder BrowseForFolder (int, string, int, Variant)
<snip>

When I leave the ModuleName in it basically returns a null value.

[12:54:54 PM] [0013] » Invoke-Pester .\test.tests.ps1
Describing functiontotest
   Context Should return null if TextFile is present
Hit Variable breakpoint on '$breakvar' (Write access)

At C:\temp\ExamineContentZip.psm1:64 char:5
+     $breakvar = $true;
+     ~~~~~~~~~~~~~~~~~
[12:54:55 PM] [0013] » $shell
[12:55:24 PM] [0022] » $shell.gettype()
You cannot call a method on a null-valued expression.
At line:1 char:1
+ $shell.gettype()
+ ~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidOperation: (:) [], RuntimeException
    + FullyQualifiedErrorId : InvokeMethodOnNull

[dlwyatt]

Ah, you're running into issue #204 . It's sort of a bug, but it's one of those things I put off fixing for a major release since it might break people's existing scripts to fix it.

In the meantime, using the InModuleScope command might be a better option. Try this instead:

Remove-Module [e]xamineContentZip -Force
$filePath = Join-Path -Path $PSScriptRoot -Child 'ExamineContentZip.psm1'
Import-Module -Name $filePath -DisableNameChecking -ErrorAction Stop

InModuleScope ExamineContentZip {
    Describe 'functiontotest' {
        Context 'Should return null if TextFile is present' {
            $zipMock = New-Module -AsCustomObject -ScriptBlock {
                function NameSpace {
                    New-Module -AsCustomObject -ScriptBlock {
                        function Items {
                            return @{Name = 'TextFile.txt'}
                        }
                    }
                }
                Export-ModuleMember -Variable * -Function *
            }

            Mock New-Object { return $zipMock } -ParameterFilter { $ComObject -eq 'Shell.Application' }

            $expected = $null;
            $returned = functiontotest -ZipFile 'Test'

            It 'Should return null' {
                $returned | should be $expected
            }
        }
    }
}

Alternatively, don't assign your object to the $zipMock variable. Just put all of that New-Module code right into the -MockWith script block, and it would work that way as well. The problem is that the -MockWith block was being executed inside the module, and the $zipMock variable was out in your test script where the module couldn't see it.

[tysonjhayes]

Crap I was afraid that's what I was running into. I tried both your suggestions and it started working. Could we highlight this in the documentation as I spent way to much time on this this morning. Totally get waiting for a major release to fix if its going to break things.

[dlwyatt]

I think it's about time to just push for the next major release; we have several of these nagging things that are waiting to be fixed.

[tysonjhayes]

Seems like a really good idea to me. This one in particular is kind of a painful bug to run into as its kind of difficult to track down exactly where the problem is.