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

Scripts/Helpers/Add-Parameter.ps1

@@ -0,0 +1,18 @@
+<#
+    .SYNOPSIS
+        Adds or updates a value in the active parameter collection.
+#>
+function Add-Parameter {
+    param (
+        $parameterName,
+        $value = $true
+    )
+
+    # Add parameter or update its value if key already exists
+    if (-not $script:Params.ContainsKey($parameterName)) {
+        $script:Params.Add($parameterName, $value)
+    }
+    else {
+        $script:Params[$parameterName] = $value
+    }
+}