Test-TrueForAll.ps1

function Test-TrueForAll {
<#
.SYNOPSIS
    Checks if all items in an array have the same value
.EXAMPLE
    'a','a','b' | Test-TrueForAll -ShouldBe 'a'
    # returns False
.EXAMPLE
    $false,$false,$false | Test-TrueForAll -ShouldBe $false
    # returns True
.EXAMPLE
    $ver1 = [version]'1.1' ; $ver2 = [version]'2.1'
    $ver1,$ver2,$ver1 | Test-TrueForAll -ShouldBe $ver1
    # returns False
.EXAMPLE
    $result1 = 'a' -eq 'a'
    $result2 = 'b' -eq 'b'
    $result3 = 'c' -eq 'c'
    $result1,$result2,$result3 | Test-TrueForAll
    # returns True
#>
[OutputType([bool])]
[CmdletBinding()]
param (
    [Parameter(Position=0)]$ShouldBe = $true,
    [Parameter(ValueFromPipeline=$true,Position=1)]$InputArray
)
Begin {
    $All = [System.Collections.Generic.List[Object]]::new()
}
Process {
    $InputArray | foreach {$All.Add($_)}
}
End {
    if ($All.Count -eq 0 -or $All.Contains($null)) {return $false}
    $Array = [array]($All | foreach {$_.ToString()})
    $Pred  = [Predicate[String]]{$args[0] -eq $ShouldBe.ToString()}
    [Array]::TrueForAll($Array,$Pred)  # <-- [bool]
} #End
} #function