Enhance validation-testing

...added because linting showed we had available testing-material that
we weren't using. May as well use it to improve robustness of the
script's validation-testing?

Author: ferricoxide

notepad-plusplus/files/npp_uninstall.ps1

@@ -21,16 +21,22 @@ if (Test-Path $Uninstaller) {
     Write-Output "Found uninstaller at '$Uninstaller'"
     Write-Output "Executing silent uninstallation..."
 
-    # Start the uninstaller with the /S (Silent) flag
+    # Start the uninstaller and capture the process object
     $Proc = Start-Process -FilePath "$Uninstaller" -ArgumentList "/S" -Wait -PassThru
 
+    # Use the variable to provide meaningful output and logic
+    Write-Output "Uninstaller exited with code: $($Proc.ExitCode)"
+
     # Optional: Wait briefly for file system hooks to release
     Start-Sleep -Seconds 2
 
-    # FINAL VERIFICATION
-    if (-not (Test-Path $NppExe)) {
+    # FINAL VERIFICATION: Check both the file system AND the exit code
+    if (-not (Test-Path $NppExe) -and $Proc.ExitCode -eq 0) {
         Write-Output "State: Success"
         exit 0
+    } elseif ($Proc.ExitCode -ne 0) {
+        Write-Error "State: Failed. Uninstaller returned non-zero exit code ($($Proc.ExitCode))"
+        exit 1
     } else {
         Write-Error "State: Failed to remove binary"
         exit 1