Add comprehensive test suite, fix minor issues, rename function and file names to match approved verbs (#708)

Tests/MainWindow-Deployment.Tests.ps1

@@ -0,0 +1,33 @@
+BeforeAll {
+    . (Join-Path $PSScriptRoot '..\Scripts\GUI\MainWindow-Deployment.ps1')
+    . (Join-Path $PSScriptRoot '..\Scripts\GUI\Get-SystemUsesDarkMode.ps1')
+}
+
+Describe 'Get-UndoFeatureLabel' {
+    BeforeEach {
+        $script:UndoFeatureLabelLookup = @{ DisableTelemetry = 'Enable telemetry' }
+        $script:FeatureLabelLookup = @{ DisableTelemetry = 'Disable telemetry'; DisableWidgets = 'Disable widgets' }
+    }
+
+    It 'prefers undo labels and falls back to feature labels' {
+        Get-UndoFeatureLabel -FeatureId 'DisableTelemetry' | Should -Be 'Enable telemetry'
+        Get-UndoFeatureLabel -FeatureId 'DisableWidgets' | Should -Be 'Disable widgets'
+    }
+
+    It 'reads selected app IDs from string or array settings and removes blanks' {
+        $stringSettings = [PSCustomObject]@{ Settings = @([PSCustomObject]@{ Name = 'Apps'; Value = ' One.App, ,Two.App ' }) }
+        $arraySettings = [PSCustomObject]@{ Settings = @([PSCustomObject]@{ Name = 'Apps'; Value = @(' One.App ', '', 'Two.App') }) }
+
+        Get-SavedAppIdsFromSettingsJson -SettingsJson $stringSettings | Should -Be @('One.App', 'Two.App')
+        Get-SavedAppIdsFromSettingsJson -SettingsJson $arraySettings | Should -Be @('One.App', 'Two.App')
+        Get-SavedAppIdsFromSettingsJson -SettingsJson ([PSCustomObject]@{ Settings = @() }) | Should -BeNullOrEmpty
+    }
+
+    It 'returns the AppsUseLightTheme registry preference and fails closed' {
+        Mock Get-ItemProperty { [PSCustomObject]@{ AppsUseLightTheme = 0 } }
+        Get-SystemUsesDarkMode | Should -BeTrue
+
+        Mock Get-ItemProperty { throw 'Registry unavailable' }
+        Get-SystemUsesDarkMode | Should -BeFalse
+    }
+}