How to mock external dll functions -New to TDD, powershell and pester, but willing to try

[Odd Erik Solberg]

I am trying to figure out how to mock an SFTP component when using Pester. Any suggestions? Should I arrange my code different?

Regards

Code

-----

Add-Type -Path (Join-Path -Path $psScriptRoot "Renci.SshNet.dll")

function Get-FromSFtp 

{

    $fileList=$null

    try

    {

        $sftp=New-Object Renci.SshNet.SftpClient("127.0.0.1","test","test")

        $sftp.Connect()

        if($sftp.IsConnected)

        {               

            $sftp.ChangeDirectory("/test")

   $fileList=$sftp.ListDirectory(".")

        }

return $fileList

    }

    catch [Exception]

    {    

        Write-Host $_.Exception.ToString()

    }

   finally

   {

if(($sftp -ne $null) -and ($sftp.IsConnected))

{

$sftp.Disconnect()

}        

   }

}

Test

Describe  "Get-FromSFtp " {

    Context "start sftp and get filelist back" {

        

        $expected=@("test.txt","test2.txt")

        

        #Not quite sure how to mock this

        #Mock something to give me the Sftp object and the expected return value

        Mock Something something??

        $actual=Get-FromSFtp 

        It "should return a list of files" {

            $actual| Should Be $expected

        }

    

    }

}

[Scott Muc]

This problem is a classic one that's found in regular application code.

The line: 

$sftp=New-Object Renci.SshNet.SFtpClient("127.0.0.1","test","test")

Needs to be wrapped by something like Get-SftpConnection which you can then mock.

Or do you just want to mock Get-FromSFtp?If that's the case, then the test isn't really testing anything except Pester's mocking functionality.

This is where TDD as a design practice shows it's strength. TDD results in easy to test code.

This looks like a good example for a TDD screencast with Pester!

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[Odd Erik Solberg]

Thanks for a really quick response.

I might be dobble posting here, but it seems that my previous post disappered.

When I moved the New-Object out to a function I still could not see how to mock the member functions 

Connect

IsConnected

ChangeDirectory

ListDirectory

Would you also move this out to functions?

Regards

Odd Erik Solberg

[scot...@gmail.com]

I finally blogged about this :-)

http://scottmuc.com/testing-powershell-code-that-talks-to-clr-objects/