(maint) Abort testing if test packages don't pack

This adds logic to the Invoke-Tests file to abort testing if packages
fail to pack. This is to improve the developer experience by not
allowing tests to run without the full set of test packages.

Invoke-Tests.ps1

@@ -57,10 +57,28 @@ if (-not (Test-Path "$TestPath/packages") -or -not $SkipPackaging) {
     $nuspecs = Get-ChildItem -Path $PSScriptRoot/src/chocolatey.tests.integration, $PSScriptRoot/tests/packages -Recurse -Include *.nuspec | Where-Object FullName -NotMatch 'bin'
     Get-ChildItem -Path $PSScriptRoot/tests/packages -Recurse -Include *.nupkg | Copy-Item -Destination "$TestPath/packages"
 
-    foreach ($file in $nuspecs) {
-        Write-Host "Packaging $file"
+    $packFailures = foreach ($file in $nuspecs) {
         # Include allow-unofficial in case an unofficial Chocolatey has been installed globally for testing
-        $null = choco pack $file.FullName --out "$TestPath/packages" --allow-unofficial
+        $packOutput = choco pack $file.FullName --out "$TestPath/packages" --allow-unofficial
+        if ($LASTEXITCODE -ne 0) {
+            [pscustomobject]@{
+                Package = $file.FullName
+                ExitCode = $LASTEXITCODE
+                Output = $packOutput
+            }
+            Write-Warning "Failed to pack $file"
+        }
+        else {
+            Write-Host "Packaged $file"
+        }
+    }
+
+    if ($null -ne $packFailures) {
+        foreach ($failure in $packFailures) {
+            Write-Warning "$($failure.Package) failed to pack with exit code: $($failure.ExitCode)"
+            $failure.Output | Write-Warning
+        }
+        throw "$($packFailures.Count) packages failed to pack."
     }
 }