test-path returns permission denied - how to do error handling

Somewhat confusingly Test-Path actually generates an error in a number of cases. Set the standard ErrorAction parameter to SilentlyContinue to ignore it.

if ((Test-Path $Db -ErrorAction SilentlyContinue) -eq $false) {

I cannot answer directly. So this has to do:

I strongly disagree with your answer. Test-Path does show $false when you run it against a network share that is not accessible, but it will be false also (without Exception) when the Server is not reachable.

So your answer simply ignores anything but a reachable share.

What is neccessary however is a try-catch-block that handles this better:

[cmdletbinding()]param(    [boolean]$returnException = $true,    [boolean]$returnFalse = $false)## Try-Catch Block:try {    if ($returnException) {        ## Server Exists, but Permission is denied.        Test-Path -Path "\\Exists\Data\" -ErrorAction Stop | Out-Null    } elseif ($returnFalse) {        ## Server does not exist        Test-Path -Path "\\NoExists\Data\" -ErrorAction Stop | Out-Null    }} catch [UnauthorizedAccessException] {    ## Unauthorized    write-host "No Access Exception"} catch {    ## an error has occurred    write-host "Any other Exception here"}

The really important part however is the ErrorAction on the Test-Path command, otherwise the exception will be wrapped around a system management error and is thus not catchable. This is in detail explained here:

PowerShell catching typed exceptions