test(WindowsRSAT): always stub install cmdlets for reliable mocking on PS 5.1

The previous BeforeAll only injected stub functions when Get-Command
found no real Install-WindowsFeature / Add-WindowsCapability. On the
Windows PowerShell 5.1 CI matrix entry, ServerManager auto-loads on
Server 2022 and the real Install-WindowsFeature is present, so the stub
was skipped. Pester then mocked the CDXML cmdlet, but the mock silently
did not intercept calls from the script under test -- all four
Server-dispatch tests reported "was called 0 times" while the rest
passed. (PS 7 matrix entries are unaffected since ServerManager does
not load on PowerShell Core, so the stub path was always taken.)

PowerShell resolves functions before cmdlets in the same scope, so
injecting the stub unconditionally lets it take precedence over the real
cmdlet, and Pester reliably mocks the function across all matrix entries.

Verified locally on Win 11 in both PowerShell 7 and Windows PowerShell
5.1: 12 passed, 0 failed, 0 skipped on both.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: tablackburn

Tests/WindowsRSAT.Type.Tests.ps1

@@ -16,17 +16,18 @@ BeforeAll {
 
     $script:ScriptPath = Join-Path $env:BHProjectPath 'PSDepend/PSDependScripts/WindowsRSAT.ps1'
 
-    # Install-WindowsFeature ships only on Windows Server (ServerManager module),
-    # and Add-WindowsCapability requires Windows. Inject stubs into the PSDepend
-    # module scope so Mock has a command to attach to on hosts that don't ship
-    # the real cmdlets (e.g. Windows client when testing the Server dispatch path).
+    # Inject stub functions for the install-side cmdlets into the PSDepend
+    # module scope so Pester's Mock attaches to a regular PowerShell function
+    # rather than to the underlying CDXML/binary cmdlets. PowerShell resolves
+    # functions before cmdlets in the same scope, so on hosts where the real
+    # cmdlets exist (Windows Server PS 5.1 with ServerManager, Windows client
+    # with DISM) the stub still wins. Mocking the real CDXML cmdlets has been
+    # observed to silently not intercept on Windows PowerShell 5.1 -- the
+    # stub-function approach makes mocking work consistently across PS 5.1,
+    # PS 7, and all platforms.
     InModuleScope PSDepend {
-        if (-not (Get-Command -Name Install-WindowsFeature -ErrorAction SilentlyContinue)) {
-            function script:Install-WindowsFeature { [CmdletBinding()] param([string]$Name) }
-        }
-        if (-not (Get-Command -Name Add-WindowsCapability -ErrorAction SilentlyContinue)) {
-            function script:Add-WindowsCapability  { [CmdletBinding()] param([switch]$Online, [string]$Name) }
-        }
+        function script:Install-WindowsFeature { [CmdletBinding()] param([string]$Name) }
+        function script:Add-WindowsCapability  { [CmdletBinding()] param([switch]$Online, [string]$Name) }
     }
 }