Why Isn't This Pester 3.4 Mock Being Called?

Question

I have a Powershell 5.1 module like this:

function CheckEventViewerForErrors(
    [string] $logName,
    [string] $logSource,
    [System.DateTime] $dateGreaterThanFilter
) {
    try {
        $logs = Get-EventLog -LogName $logName -Source $logSource 
        $errorLogs = $logs | Where-Object { 
                ($_.TimeGenerated -gt $dateGreaterThanFilter) `
                -and `
                ($_.EntryType -eq 'Error')
            }
        if ($null -ne $errorLogs) {
            return $true
        }
        return $false
    }
    catch {
        return $true
    }
}


Export-ModuleMember -Function "*"

Which I want to test using Pester 3.4.0 like below, but the mock isn't being called when I use the commented-out parameter filter.

Describe 'CheckEventViewerForErrors' {
    $logName = 'Application'
    $logSource = "Pester"
    $time = Get-Date
    $cmdToMock = 'Get-EventLog'
    $moduleName = $module.Name

    Context 'Tests using mocks' {
        # $paramFilter = { ($LogName -eq $logSource) -and ($LogName -eq $logName) }

        It 'returns $false when there are entries for the source but no errors' {
            Mock `
                -ModuleName $moduleName `
                -CommandName $cmdToMock `
                -MockWith { return @{ TimeGenerated = $time; EntryType = 'Error' } } 
                # -ParameterFilter $paramFilter 

            $expected = $false                

            [bool] $actual = CheckEventViewerForErrors `
                -logName $logName `
                -logSource $logSource `
                -dateGreaterThanFilter $time

            Assert-MockCalled -Module $moduleName -CommandName $cmdToMock # -ParameterFilter $paramFilter 
            $actual | Should Be $expected
        }
    }     
}   

What's wrong with this code?. How can I mock the use of Get-EventLog in the function exported?

This message is returned by the above test:

Expected Get-EventLog to be called at least 1 times but was called 0 times

Answer 1

There is an error in your Parameter Filter, you are filtering for LogName twice, but with different variables (hence it doesn't end up resulting in a matched use of Get-EventLog in the script):

$paramFilter = { ($LogName -eq $logSource) -and ($LogName -eq $logName) }

If I change it to this, you code works for me:

$paramFilter = { ($LogSource -eq $logSource) -and ($LogName -eq $logName) }