How to test a function within a script

[DarkLite1]

This is more a question than it is an issue. Suppose I have a script file that contains some functions in the Begin clause. However, the script has also some actions defined in the Process clause and some mandatory parameters in the Parameters.

Under normal circumstances I would move the functions to a module and test the module for proper functionality of the containing functions. But in this case, that's not possible. Because we need these functions to be in the script file. The script file will later be called with Invoke-Command -FilePath Script.ps1 -ComputerName xxx to run on remote machines where there's no module folder available.

Consider the following example:

Param (
    [Parameter(Mandatory)]
    [String]$Name
)

Begin {
    Function Test-NumberIsFive {
        Param (
            [Parameter(Mandatory)]
            [Int]$Number
        )

        if ($Number -eq 5) {
            $true
        }
    }
}

Process {
    (0..10).ForEach({ Test-NumberIsFive -Number $_ })
}

What is the best way to test the function Test-NumberIsFive without invoking the script?

[alexjordan6]

Hey, this is pretty similar to #247, want to give that a read?

[nohwnd]

@DarkLite1 I wrote this concept a while ago, maybe you can do something with it. Pretty much it just manipulates your script to have a main function so that your script is just functions, and then puts stuff back where it was. This way the script becomes testable for a moment, and then becomes shippable again.

[DarkLite1]

Thx guys I'll give it a go 👍

[DarkLite1]

It would be really cool if there was something like this:
Mock Test-NumberIsFive -InScriptScope
Just a bit like Mock -ModuleName

[dlwyatt]

Not possible, I'm afraid. If there's no break between the code that loads the function and the code that calls it, Pester doesn't have any chance to inject mocks.

[DarkLite1]

In the meantime I found a workaround:

it 'No new ticket is created when the place holder account is present in the group' {
    Function Get-GroupMemberHC {}

    Mock Get-GroupMemberHC {
        @('Bob', 'jake')
    }

    . "$here/$sut" @TestParams

    Assert-MockCalled New-TicketHC -Times 0 -Exactly -Scope It
}

I just create a dummy Function in the Pester test file before I call the Mock in the It clause. That seems to do the trick. In the example above the function Get-GroupMember is created in the Begin clause of the production script.

[dlwyatt]

That’s a good point. We used to create mock functions that would be overwritten when the script ran in your example, but now we use aliases instead.

…

On Sep 20, 2018, at 9:22 AM, DarkLite1 ***@***.***> wrote: In the meantime I found a workaround: it 'No new ticket is created when the place holder account is present in the group' { Function Get-GroupMemberHC {} Mock Get-ADGroup -MockWith { @{ DistinguishedName = 'Group 1' } } Mock Get-GroupMemberHC { @($TestParams.PlaceHolderAccount, 'jake') } . "$here/$sut" @TestParams Assert-MockCalled New-TicketHC -Times 0 -Exactly -Scope It } Is just create the Function again before I call the Mock in the It clause. That seems to do the trick. — You are receiving this because you commented. Reply to this email directly, view it on GitHub, or mute the thread.

[nohwnd]

@DarkLite1 @dlwyatt 😮 omg that's right... So that also means we can use it with & operator, as long as the aliases are not overwritten.

# --- file t1.ps1 
param (
    [Parameter(Mandatory)]
    $name
)

function a {
    param ($name) 
    Write-Host "this is $name"
}

a $name

# --- file t1.tests.ps1
Describe "mock in script" {
    It "mocks a" {
        function a () {}
        mock a { Write-Host "this is mock" }
        # notice that I am invoking it with & here
        & "$psScriptRoot/t1.ps1" -name "jakub"

        Assert-MockCalled a -Exactly 1
    }
}

## output.ps1
# Describing mock in script
# this is mock
#  [+] mocks a 103ms

[nohwnd]

Now two problems remain to solve:

• mandatory params
• executing the code in body of the script

The solutions could be following:

• params -> provide them yourself, or we could AST the script and provide defaults (if available), but that takes a bit of work

• code in body -> place your code in an entry point function and invoke it at the end. (e.g. Main)
  You can alias the entry function, dot-source the script, then remove the alias. At that point you have all your functions in scope, including Main, and they are all linked to the correct invocation info. You can then proceed to mock as usual and unit test your functions, while keeping the script self-contained.

like this:

###  --- file t1.ps1
param (
    [Parameter(Mandatory)]
    $Name
)

# our entry point function that holds 
# all the stuff that should happen when 
# we run this script
function Main {
    param (
        [Parameter(Mandatory)]
        $Name
    )
    Write-Host $PSCommandPath
    Get-Greeting $Name
}

# internal function that writes greeting
function Get-Greeting {
    param ($Name) 

    $text = Get-GreetingText 
    $formattedGreetingText = $text -f $Name
    Write-Host $formattedGreetingText
    $formattedGreetingText
}

# another internal function that collaborates
# with Get-Greeting and that we will mock 
# in our tests
function Get-GreetingText {
    'Hello, {0}!'
}

Main -Name $Name

### --- file t1.tests.ps1
&{
    # invoking the script directly to see it's 
    # still doing what it should
    &"$psScriptRoot/t1.ps1" -Name 'Thomas'
}
& {
    #### 
    # the following code would be body of a func, but then the dot-sourced
    # functions would die within the scope of that function
    # this can imho be solved by the same approach I am taking 
    # in my Mock repo - doing what iex is doing internally
    # Import-Script -EntryPoint Main -Path "$psScriptRoot/t1.ps1"


    # mock the entrypoint function so
    # we don't run anything from the script
    $EntryPoint = 'Main'
    $Path = "$psScriptRoot/t1.ps1"
    Invoke-Expression 'function placeholder { Write-Host "this is placeholder" }'
    # alias to prevent main from running
    Set-Alias $EntryPoint 'placeholder'

    . $Path -Name 'Jakub'
    # remove the alias, now we have all functions
    # from the script dot-sourced in this scope
    Remove-Item "alias:$EntryPoint" -Force
    ####

    Describe "t1.ps1" {
        It "Can test 'Main' function" {
            Main -Name 'Pester' | Should -Be 'Hello, Pester!'
        }

        It "Can test 'Get-Greeting' function" {
            Get-Greeting -Name 'Pester' | Should -Be 'Hello, Pester!'
        }

        It "Can mock Get-GreetingText that is used by Get-GreetingFunction" {
            Mock Get-GreetingText { '{0} is getting better at mocking!'  }
            Get-Greeting -Name 'Pester' | Should -Be 'Pester is getting better at mocking!'
        }
    }
}

/Users/nohwnd/Desktop/t1.ps1
Hello, Thomas!
Hello, Thomas!
this is placeholder

Describing t1.ps1
/Users/nohwnd/Desktop/t1.ps1
Hello, Pester!
  [+] Can test 'Main' function 58ms
Hello, Pester!
  [+] Can test 'Get-Greeting' function 34ms
Pester is getting better at mocking!
  [+] Can mock Get-GreetingText that is used by Get-GreetingFunction 65ms

One small problem with this, if you encapsulate the steps into a helper function (say Import-Script) then you will dot-source into the scope of Import-Script and your functions won't be available for testing. I will test this using iex, and if that works, then I can encapsulate it in binary cmdlet, that does when iex does + the extra aliasing behavior.

[nohwnd]

@DarkLite1 🎉 🍾 👍 Can you confirm it works? Tested only on PSCore on macOs.

Add-Type -TypeDefinition @'
using System.Collections.ObjectModel;
using System.Management.Automation;
using System.Reflection;

namespace ScriptMocking
{
    [Cmdlet(VerbsData.Import, "Script")]
    public sealed class ImportScriptCommand : PSCmdlet
    {
        private static string Body = @"
            function ____placeholder {{ }}
            # alias to prevent main from running
            Set-Alias {0} '____placeholder'
            
            . {1} {2}
            # remove the alias, now we have all functions
            # from the script dot-sourced in this scope
            Remove-Item 'alias:{0}' -Force
            Remove-Item 'function:____placeholder' -Force";

        [Parameter(Position = 0, Mandatory = true)]
        public string Path { get; set; }

        [Parameter(Position = 1)]
        public string EntryPoint { get; set; }

        [Parameter]
        public string[] ArgumentList { get; set; }

        public ImportScriptCommand() {
            ArgumentList = new string[0];
            EntryPoint = "Main";
        }
        protected override void ProcessRecord()
        {
            var body =  string.Format(Body, EntryPoint, Path, string.Join(" ", ArgumentList));

            var sb = InvokeCommand.NewScriptBlock(body);

            var method = sb.GetType()
                .GetMethod("InvokeUsingCmdlet", BindingFlags.Instance | BindingFlags.NonPublic);

            var emptyArray = new object[0];
            var automationNull = new PSObject();
            const int writeToCurrentErrorPipe = 1;

            var @params = new object[]
                {this, false, writeToCurrentErrorPipe, automationNull, emptyArray, automationNull, new object[0]};

            method.Invoke(sb, @params);
        }
    }
}
'@

Import-Module ([ScriptMocking.ImportScriptCommand].Assembly)
Import-Script -Path "$psScriptRoot/t1.ps1" -EntryPoint 'Main' -ArgumentList '-Name Jakub'

Describe "t1.ps1" {
    It "Can test 'Main' function" {
        Main -Name 'Pester' | Should -Be 'Hello, Pester!'
    }

    It "Can test 'Get-Greeting' function" {
        Get-Greeting -Name 'Pester' | Should -Be 'Hello, Pester!'
    }

    It "Can mock Get-GreetingText that is used by Get-GreetingFunction" {
        Mock Get-GreetingText { '{0} is getting better at mocking!'  }
        Get-Greeting -Name 'Pester' | Should -Be 'Pester is getting better at mocking!'
    }
}

[DarkLite1]

Hi @nohwnd , when I run your example in your second last post with file t1.ps1 and file t1.Tests.ps1 it is successful. However, When I try your last post and put it all in file t1.Tests.ps1 (the part with Add-Type) it fails:

[Add-Type : c:\Users\me\AppData\Local\Temp\39\cvdeisu1\cvdeisu1.0.cs(25) : Invalid token '=' 
in class, struct, or interface member declaration
c:\Users\,\me\AppData\Local\Temp\39\cvdeisu1\cvdeisu1.0.cs(24) :         [Parameter(Position =
 1)]
c:\Users\me\AppData\Local\Temp\39\cvdeisu1\cvdeisu1.0.cs(25) : >>>         public string Ent
ryPoint { get; set; } = "Main";
c:\Users\me\AppData\Local\Temp\39\cvdeisu1\cvdeisu1.0.cs(26) : 
At S:\Test\me\Pester\t1.tests.ps1:1 char:1](url)

I think I might have misunderstood how you wanted me to test...

[nohwnd]

@DarkLite1 seem that PowerShell 5 supports only older C# syntax, fixed the code.

[DarkLite1]

Can you verify the edit you made? I only get red errors when copying the code starting with using System.Collections.ObjectModel; ... in the file t1.tests.ps1.

[nohwnd]

@DarkLite1 should be fixed now, I did not copy the first line.

[DarkLite1]

No prob, works perfectly fine now. Thank you for your help :)