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

Tests/Get-FriendlyRegistryBackupTarget.Tests.ps1

@@ -0,0 +1,21 @@
+BeforeAll {
+    $friendlyTargetScriptPath = Join-Path $PSScriptRoot '..\Scripts\Helpers\Get-FriendlyRegistryBackupTarget.ps1'
+    . $friendlyTargetScriptPath
+}
+
+Describe 'Get-FriendlyRegistryBackupTarget' {
+    It 'formats <Case> as <Expected>' -ForEach @(
+        @{ Case = 'a null target'; Target = $null; Expected = 'Unknown' }
+        @{ Case = 'the default profile'; Target = 'DefaultUserProfile'; Expected = 'Default user profile' }
+        @{ Case = 'the current-user marker'; Target = 'CurrentUser'; Expected = 'Current user' }
+        @{ Case = 'the all-users marker'; Target = 'AllUsers'; Expected = 'All users' }
+        @{ Case = 'a named current user'; Target = 'CurrentUser:Alice'; Expected = 'Current user (Alice)' }
+        @{ Case = 'a named target user'; Target = 'User:Bob'; Expected = 'User (Bob)' }
+    ) {
+        Get-FriendlyRegistryBackupTarget -Target $Target | Should -Be $Expected
+    }
+
+    It 'keeps unrecognized target text visible to the user' {
+        Get-FriendlyRegistryBackupTarget -Target 'Custom:Value' | Should -Be 'Custom:Value'
+    }
+}