test: update Windows CSE helper UT (#4924)

parts/windows/windowscsehelper.ps1

@@ -72,6 +72,9 @@ $global:WINDOWS_CSE_ERROR_INSTALL_CREDENTIAL_PROVIDER = 65 # exit code for insta
 $global:WINDOWS_CSE_ERROR_DOWNLOAD_CREDEDNTIAL_PROVIDER=66 # exit code for downloading credential provider failure
 $global:WINDOWS_CSE_ERROR_CREDENTIAL_PROVIDER_CONFIG=67 # exit code for checking credential provider config failure
 $global:WINDOWS_CSE_ERROR_ADJUST_PAGEFILE_SIZE=68
+# WINDOWS_CSE_ERROR_MAX_CODE is only used in unit tests to verify whether new error code name is added in $global:ErrorCodeNames
+# Please use the current value of WINDOWS_CSE_ERROR_MAX_CODE as the value of the new error code and increment it by 1
+$global:WINDOWS_CSE_ERROR_MAX_CODE=69
 
 # Please add new error code for downloading new packages in RP code too
 $global:ErrorCodeNames = @(

parts/windows/windowscsehelper.tests.ps1

@@ -133,6 +133,9 @@ Describe 'Get-WindowsVersion and Get-WindowsPauseVersion' {
 
 Describe 'Validate Exit Codes' {
   It 'should succeed' {
+    Write-Host "Validating whether new error code name is added with the new error code"
+    $global:ErrorCodeNames.Length | Should -Be $global:WINDOWS_CSE_ERROR_MAX_CODE
+
     for($i=0; $i -lt $global:ErrorCodeNames.Length; $i++) {
       $name=$global:ErrorCodeNames[$i]
       $name | Should -Match '[A-Z_]+'