stop on BITS download errors

reject 0 byte dsa-collector.exe before launching

tests/Get-DSAManifest.Tests.ps1

@@ -13,12 +13,18 @@ Function Download-File {
     [CmdletBinding()]
     param($URL, $File)
     $script:DsaDownloadCalls++
+    If ($script:DsaTestMode -eq 'empty-download') {
+        [IO.File]::WriteAllBytes($File, [byte[]]@())
+        Return $File
+    }
+    If ($script:DsaTestMode -eq 'download-failure') { Throw 'Simulated BITS failure.' }
     [IO.File]::WriteAllText($File, 'Mock executable; never executed.')
     Return $File
 }
 Function Start-Process {
     [CmdletBinding()]
     param($FilePath, $ArgumentList, [switch]$Wait, [switch]$PassThru, $WindowStyle)
+    $script:DsaProcessCalls++
     $DsaMatch = [regex]::Match($ArgumentList, '"--output"\s+"([^"]+)"')
     If (!$DsaMatch.Success) { Throw 'Collector output argument missing.' }
     $script:DsaCsvPath = $DsaMatch.Groups[1].Value
@@ -64,6 +70,7 @@ Function Invoke-DsaCase {
     $script:DsaTestMode = $Mode
     $script:DsaRecordedUploads = @()
     $script:DsaDownloadCalls = 0
+    $script:DsaProcessCalls = 0
     $script:DsaGeneratedPath = $null
     $DsaCaught = $null
     Try { . $DsaScriptUnderTest | Out-Null } Catch { $DsaCaught = $_ }
@@ -73,6 +80,14 @@ Function Invoke-DsaCase {
         Assert-Dsa ($script:DsaDownloadCalls -eq 0) 'Invalid flag must fail before downloading.'
         Return
     }
+    If ($Mode -in @('empty-download','download-failure')) {
+        Assert-Dsa ($null -ne $DsaCaught) 'Download failure must stop collection.'
+        Assert-Dsa ($script:DsaProcessCalls -eq 0 -and $script:DsaRecordedUploads.Count -eq 0) 'Download failure must prevent execution and upload.'
+        If ($Mode -eq 'empty-download') {
+            Assert-Dsa ($DsaCaught.Exception.Message -like '*0 bytes*') 'Empty download error must explain the failure.'
+        }
+        Return
+    }
     If ($Mode -in @('collector-failure','missing-output')) {
         Assert-Dsa ($null -ne $DsaCaught -and $script:DsaRecordedUploads.Count -eq 0) 'Collection failure must prevent upload.'
         Return
@@ -107,7 +122,7 @@ Try {
                 Write-Host "PASS: ZIP=$ZipExpected Upload=$UploadExpected DeleteAfterUpload=$DeleteExpected"
             }
         }
-        Foreach ($Mode in @('upload-failure','no-receipt','incomplete-receipt','collector-failure','missing-output')) {
+        Foreach ($Mode in @('upload-failure','no-receipt','incomplete-receipt','collector-failure','missing-output','empty-download','download-failure')) {
             Invoke-DsaCase $ZipExpected $true $true $Mode
             Write-Host "PASS: ZIP=$ZipExpected $Mode prevents deletion."
         }