How to mock a job in Pester?

Question

We're trying to assess if Invoke-Command has been called exactly one time.

Script.ps1

$job = Invoke-Command -ScriptBlock {'test'} -ComputerName localhost -AsJob 
$job | Wait-Job

Script.Tests.ps1

BeforeAll {
    $testScript = $PSCommandPath.Replace('.Tests.ps1', '.ps1')
    Mock Invoke-Command
}
Describe 'Test' {
    It 'should be green' {
        . $testScript
        Should -Invoke Invoke-Command -Times 1 -Exactly -Scope It
    }
}

The problem is mocking the job object in Pester. When the job is not mocked, Wait-Job will throw an error that it didn't receive a job object.

How is it possible to mock a PowerShell job object in Pester?

score 9 · Accepted Answer · answered Jul 16 '18 at 12:31

9

One solution might be to have the Mock of Invoke-Command still create a legitimate job, but executing some script/code that you deem safe for the purpose of testing.

To do this, you need to first put the Invoke-Command cmdlet in a variable so that you can use it via that variable (because a Mock can't directly call its own command).

For example:

$InvokeCommand = Get-Command Invoke-Command

Mock Invoke-Command {
     & $InvokeCommand -ScriptBlock {'some safe alternative code'} -ComputerName localhost -AsJob
}

answered Jul 16 '18 at 12:31

Mark Wragg

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This is Nice. Neat and clean approach. – Ranadip Dutta Jul 16 '18 at 12:42
1

I didn't know this was possible. Like you said, it kept calling its own `Mock`. Love your solution! Big thumbs up Mark :) – DarkLite1 Jul 16 '18 at 12:45
1

Excellent solution. – toose121 Dec 17 '20 at 22:32

How to mock a job in Pester?

1 Answers1