feat: Add Windows guest helper tests and update Makefile

- Introduced Pester tests for the Windows guest helper script (`filerestore.bat`).
- Updated Makefile to include a new target for running Windows tests.
- Created `TESTING.md` for Windows guest helper with instructions on running tests.
- Refactored `filerestore.bat` to support testing and improve argument parsing.
- Added `TestHelper.psm1` for shared functions used in Pester tests.
- Implemented comprehensive Pester tests covering various scenarios for the Windows guest helper.

Signed-off-by: Emanuele Prella <eprella@redhat.com>

Author: ema-aka-young

Makefile

@@ -168,12 +168,27 @@ test-e2e: manifests generate fmt vet ## Run e2e tests (requires kubevirtci clust
 ##@ Script Tests
 
 CONTAINER_ENGINE ?= $(CONTAINER_TOOL)
+# mcr.microsoft.com/powershell is deprecated; the .NET SDK image is the
+# recommended replacement and includes pwsh.
+# https://learn.microsoft.com/en-us/powershell/scripting/install/powershell-in-docker
+PWSH_IMAGE ?= mcr.microsoft.com/dotnet/sdk:9.0
+PESTER_VERSION ?= 5.7.1
 BATS_IMAGE ?= bats/bats:1.13.0
 # :Z relabels for SELinux; use empty value on Docker Desktop (macOS/Windows)
 VOLUME_OPTS ?= :Z
 
 .PHONY: test-scripts
-test-scripts: test-scripts-linux ## Run guest-helper script tests
+test-scripts: test-scripts-windows test-scripts-linux ## Run guest-helper script tests
+
+.PHONY: test-scripts-windows
+test-scripts-windows: ## Run Pester tests for Windows guest helper (containerized)
+	$(CONTAINER_ENGINE) run --rm \
+		-v $(shell pwd):/workspace$(VOLUME_OPTS) \
+		-w /workspace \
+		$(PWSH_IMAGE) \
+		pwsh -NoProfile -Command " \
+			Install-Module Pester -RequiredVersion $(PESTER_VERSION) -Force -SkipPublisherCheck -Scope CurrentUser; \
+			Invoke-Pester -Path 'guest-helpers/windows/test/' -Output Detailed -CI"
 
 .PHONY: test-scripts-linux
 test-scripts-linux: ## Run BATS tests for Linux guest helper (containerized)

guest-helpers/linux/TESTING.md

@@ -7,13 +7,13 @@ Unit tests for the Linux guest helper script (`filerestore.sh`).
 Run script tests (requires Docker or Podman):
 
 ```bash
-make test-scripts
+make test-scripts-linux
 ```
 
 By default, `CONTAINER_ENGINE` inherits from `CONTAINER_TOOL`, which defaults to `docker`. To override:
 
 ```bash
-CONTAINER_ENGINE=docker make test-scripts
+CONTAINER_ENGINE=docker make test-scripts-linux
 ```
 
 ## Prerequisites

guest-helpers/windows/TESTING.md

@@ -0,0 +1,47 @@
+# Guest Helper Script Tests
+
+Unit tests for the Windows guest helper script (`filerestore.bat`).
+
+## Quick Start
+
+Run script tests (requires Docker or Podman):
+
+```bash
+make test-scripts-windows
+```
+
+By default, `CONTAINER_ENGINE` inherits from `CONTAINER_TOOL`, which defaults to `docker`. To override:
+
+```bash
+CONTAINER_ENGINE=docker make test-scripts-windows
+```
+
+## Prerequisites
+
+Only a container runtime (Docker or Podman) is needed:
+
+- [`mcr.microsoft.com/dotnet/sdk`](https://learn.microsoft.com/en-us/powershell/scripting/install/powershell-in-docker) with [Pester v5](https://pester.dev/) installed at runtime (pinned version; requires network access to the PowerShell Gallery)
+
+No local installation of PowerShell or Pester is required (the container downloads Pester on demand).
+
+## Test Structure
+
+```
+guest-helpers/windows/
+  filerestore.bat
+  test/
+    filerestore.Tests.ps1     # Pester test cases
+    TestHelper.psm1           # Script extraction, Windows cmdlet stubs
+```
+
+## How the Tests Work
+
+The test helper extracts the PowerShell portion from the bat/PS polyglot file
+by stripping the batch preamble (everything up to the closing `#>` block
+comment marker). The extracted script is dot-sourced, which triggers a
+`$MyInvocation.InvocationName` guard that loads all function definitions
+without executing the main entry point.
+
+Windows-only cmdlets (`Get-Disk`, `Set-Disk`, `Get-Partition`, etc.) are
+defined as stub functions with proper parameter declarations, enabling Pester's
+`Mock` and `Should -Invoke` to work on Linux.