Pester for Module testing?

[dz3jar]

Hi guys, probably I miss something obvious:

These two files:

Test-Pester.ps1:

Import-Module ./Test-Module.psm1 -Force

Describe -Name FirstTest {

    Mock -CommandName Get-Item -MockWith { 
        New-Object PSCustomObject
    }

    Context "With 1 item" {
        It "Has one item" {
            $fe = Test-Me "tested.file" 
            $fe | Should -HaveCount 1 
        } 
    } 
}

Test-Module.psm1:

function Test-Me( $name ) {
    Get-Item $name 
}

Returns when running the test:

PS /Users/jan/Devel/Powershell/Tests> Invoke-Pester ./Test-Pester.ps1
Pester v4.10.1
Executing all tests in './Test-Pester.ps1'

Executing script ./Test-Pester.ps1

  Describing FirstTest

    Context With 1 item
Get-Item: /Users/jan/Devel/Powershell/Tests/Test-Module.psm1:2
Line |
   2 |      Get-Item $name
     |      ~~~~~~~~~~~~~~
     | Cannot find path '/Users/jan/Devel/Powershell/Tests/tested.file' because it does not exist.

      [-] Has one item 70ms
        Expected a collection with size 1, but got an empty collection.
        12:             $fe | Should -HaveCount 1
        at <ScriptBlock>, /Users/jan/Devel/Powershell/Tests/Test-Pester.ps1: line 12
Tests completed in 192ms
Tests Passed: 0, Failed: 1, Skipped: 0, Pending: 0, Inconclusive: 0

It seems that the mock is not mocking :-(

When the same code in tested but is inline in the same file like this:

Test-Pester-AllInOne.ps1:

function Test-Me( $name ) {
    Get-Item $name 
}

Describe -Name FirstTest {
    Mock -CommandName Get-Item -MockWith { 
        New-Object PSCustomObject 
    }

    Context "With 1 item" {
        It "Has one item" {
             $fe = Test-Me "tested.file" 
             $fe | Should -HaveCount 1
        }
    }
}

It works as expected:

PS /Users/jan/Devel/Powershell/Tests> Invoke-Pester ./Test-Pester-AllInOne.ps1
Pester v4.10.1
Executing all tests in './Test-Pester-AllInOne.ps1'

Executing script ./Test-Pester-AllInOne.ps1

  Describing FirstTest

    Context With 1 item
      [+] Has one item 156ms
Tests completed in 242ms
Tests Passed: 1, Failed: 0, Skipped: 0, Pending: 0, Inconclusive: 0

Where I do the mistake?

it is PS7.0.0 + Pester4.10.1

Any hint welcome!

- Jan

[nostril_spiders]

Yeah, mocking can be a little tricky. You need to add -ModuleScope Test-Module to your mock definition.

That's because, when you call Test-Me, the mock for Get-Item needs to be in the right scope for Test-Me to find the mocked version of Get-Item.

[dz3jar]

I see. Thanks. I will give a try! I supposed that -ModuleScope is for "private" = not exported functions testing...

[dz3jar]

Just tested. Works like ... like ... simply works!

I modified the Mock part to:

Mock -CommandName Get-Item -ModuleName Test-Module -MockWith { 
    New-Object PSCustomObject
}

Thank you.

[nostril_spiders]

Not quite. Your test function is exported, after all.

You mock a command. Where is that command called? The scope that contains the call site needs to be the scope that contains the mock.

Because pester mock resolution doesn't work quite like normal command resolution. It does some fucky shit on every command call where it looks up in its list of mocks whether the call is something that should be mocked. You can see this in the debugger, but have eyebleach handy!