Pester test if the module is existing. Should not throw specific ExceptionType

Question

Is it only me or the Pester if extremely hard to grab?

In the BeforeAll scriptblock I would like to test if the ActiveDirectory module is existing on the local machine.

The test should not throw exception type [System.IO.FileNotFoundException]

Question 1:

What is the correct/best approach?

Get-Module Module| Remove-Module -Force
Import-Module Module
Import-Module Pester

InModuleScope Module{

    Describe 'Add-Patchgroup' {

        BeforeAll {
            It 'Should import module ActiveDirectory' {
                {Import-Module -Name ActiveDirectory -ErrorAction Stop } | Should -Not -Throw -ExceptionType {[System.IO.FileNotFoundException]}
            }
        }
    }
}

Error when I run this on machine where AD module is not available:

Describing Add-Patchgroup
  [-] Should import module ActiveDirectory 99ms
    PSInvalidCastException: Cannot convert the "[System.IO.FileNotFoundException]" value of type "System.Management.Auto
mation.ScriptBlock" to type "System.Type".
    ArgumentTransformationMetadataException: Cannot convert the "[System.IO.FileNotFoundException]" value of type "Syste
m.Management.Automation.ScriptBlock" to type "System.Type".
    ParameterBindingArgumentTransformationException: Cannot process argument transformation on parameter 'ExceptionType'
. Cannot convert the "[System.IO.FileNotFoundException]" value of type "System.Management.Automation.ScriptBlock" to typ
e "System.Type".

Question 2:

Also consider there is a module named ComplexModule which is very time consuming to Import. Therefore I would like to mock the Import-Module -Name ComplexModule cmdlet. How can I do it?

score 2 · Accepted Answer · answered Jul 24 '18 at 14:17

2

Your test for whether an exception has been thrown needs to specify the exception as a string:

It 'Should import module ActiveDirectory' {
    {Import-Module -Name ActiveDirectory -ErrorAction Stop } | Should -Not -Throw -ExceptionType System.IO.FileNotFoundException
}

You could Mock your Import-Module as follows:

Mock Import-Module {} -ParameterFilter {$Name -eq 'ComplexModule'}

Beware that you may have issues using Import-Module successfully/legitimately in your Pester script after you've mocked it, but so long as you use it before the Mock I think you'll be OK.

Note also that this Mock does nothing (hence the empty {}) so it effectively ensures the module is not loaded. If your tests rely on the module being loaded, you'll need to either not Mock it or find a way to load the needed commands otherwise.

answered Jul 24 '18 at 14:17

Mark Wragg

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modified my code but still not passing: [-] Should import module ActiveDirectory 82ms Expected no exception to be thrown, but an exception "The specified module 'ActiveDirectory' was not loaded because no valid module file was found in any module directory." was thrown from line:11 char:18 – pandemic Jul 24 '18 at 14:21
Suggests where you are running the test the AD module is not available. – Mark Wragg Jul 24 '18 at 14:22
running the test where the AD module is not available. here is the prtscr: https://ibb.co/mDaVb8 (do not mind other tests) – pandemic Jul 24 '18 at 14:25
So you've written a test that checks that `Import-Module ActiveDirectory` does not throw a file not found exception. It does throw a file not found exception because its not installed on your system, hence your test fails, hence you get red text. – Mark Wragg Jul 24 '18 at 14:26
ohhh! *blushing* *facepalm* – pandemic Jul 24 '18 at 14:30

Pester test if the module is existing. Should not throw specific ExceptionType

1 Answers1