The alias solution you posted is clever, but I would argue against its use in scripts, for the same reason I don't like using any aliases in scripts; it tends to harm readability.
If this is something you want to add to your profile so you can type out quick commands or use it as a shell, then I could see that making sense.
You might consider piping instead:
if ($path | Test-Path) { ... }
if (-not ($path | Test-Path)) { ... }
if (!($path | Test-Path)) { ... }
Alternatively, for the negative approach, if appropriate for your code, you can make it a positive check then use else
for the negative:
if (Test-Path $path) {
throw "File already exists."
} else {
# The thing you really wanted to do.
}