Pester - Mocking a function with a parameter of type System.Array

Pester has a very cool Mock function that allows you to replace a function with a Mocked function, which you can then test to see if it’s run with certain parameters.

I have been trying to improve the test coverage of PSForge, but I hit a snag when I was trying to create a Mock with a ParameterFilter that checks a parameter that contains an array. The following code did not work;

Mock Invoke-ExternalCommand { return "/fake-path" } -ParameterFilter { $Command -eq "git" -and $Arguments -eq @("rev-parse", "--show-toplevel"))}

This is due to the fact that Powershell’s -eq operator doesn’t support checking if two arrays are equal.

To get around this, I wrote a very quick and dirty function that checks if two sorted arrays are equal;

function Compare-Array {
    $($args[0] -join ",") -eq $($args[1] -join ",")

If the arrays are not sorted prior, they will not match.

The working Mock

Once I had declared the Compare-Array function, the following command successfully mocked the function with the array parameter.

Mock Invoke-ExternalCommand { return "/fake-path" } -ParameterFilter { $Command -eq "git" -and (Compare-Array $Arguments @("rev-parse", "--show-toplevel"))}

For a more bells-and-whistles implementation of Compare-Array, you could try this version.

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