Is there a way to mock an $? return using Pester?

Question

I'm writing tests for a PowerShell application, using Pester.

I have been able to create mocks for most functions, but I haven't been able to mock a function returning the $? variable. I'm currently using it to evaluate the returns from AWS CLI commands.

This is, for example, to mock a failing AWS CLI command return.

Any thoughts?

$_ Usually is just the current item you are working with. Can you give some examples of what you are trying to mock? — Ben Richards, Jun 06 '17 at 16:13
@BenRichards `$?` returns `true/false` depending on if the last command ran without errors. — colsw, Jun 06 '17 at 16:19

score 2 · Answer 1 · edited Dec 19 '18 at 09:23

If you're looking to get mock code which performs the same function as $?, you can use something like this (it is quite limited in terms of how it actually returns if multiple lines are executed at once, etc., and it will likely need to be modified depending on the execution context):

Function Test-LastCommandError {
    $LastCommand = (History | Select -Last 1).CommandLine
    $LastError = $Error[-1].InvocationInfo.Line
    $LastCommand -eq $LastError
}

1/1#Success
Test-LastCommandError # Returns false

1/0#Error
Test-LastCommandError # Returns true

This works for me manually executing each line, but not in an ad-hoc ISE window (since it copy-pastes everything as one command on execute).

score 1 · Accepted Answer · edited Dec 19 '18 at 12:36

We created an auxiliary function and passed the $? value.

function Test-LastExitCodeIsFalse ($last_exit) {
    if ($last_exit) {
       return $false
    }
    $true
}

And a usage being

aws s3 <an aws command>
if (Test-LastExitCodeIsFalse($?)) {
   throw "AWS Exception"
}

Using Pester, then we just mock the Test-LastExitCodeIsFalse function to return false. And we have a unit test with a failing AWS instance :)

score 0 · Answer 3 · answered Jun 06 '17 at 16:21

0

You should be able to do:

Mock AWC-CLI { $ = $true } -Verifiable

answered Jun 06 '17 at 16:21

Ben Richards

3,437
1
14
18

Is there a way to mock an $? return using Pester?

3 Answers3