Private/TestCsvHeaderExists.ps1

function TestCsvHeaderExists {
    [OutputType([bool])]
    [CmdletBinding()]
    param
    (
        [Parameter(Mandatory)]
        [ValidateNotNullOrEmpty()]
        [string]$CsvFilePath,

        [Parameter()]
        [ValidateNotNullOrEmpty()]
        [object[]]$Header,

        [Parameter()]
        [ValidateNotNullOrEmpty()]
        [switch]$ParseScriptBlockHeaders
    )

    $csvHeaders = GetCsvColumnHeaders -CsvFilePath $CsvFilePath

    ## Parse out the CSV headers used if the field is a scriptblock
    $commonHeaders = @($Header).foreach({
            $_ | ForEach-Object {
                if ($_ -is 'scriptblock') {
                    ## It's extremely hard to figure out what values inside of the scriptblock are actual CSV headers
                    ## Give the option here.
                    if ($ParseScriptBlockHeaders.IsPresent) {
                        ParseScriptBlockHeaders -FieldScriptBlock $_
                    }
                } else {
                    $_
                }
            }
        })

    ## Assuming that ParseScriptBlockHeaders was not used and all of the headers
    ## are scriptblocks. We check nothing but still return true.
    if (-not ($commonHeaders = $commonHeaders | Select-Object -Unique)) {
        $true
    } else {
        $matchedHeaders = $csvHeaders | Where-Object { $_ -in $commonHeaders }
        if (@($matchedHeaders).Count -ne @($commonHeaders).Count) {
            $false
        } else {
            $true
        }
    }
}