Check out the Macro Console under the System app. System > Macros > Console. That will allow you to test macros with virtual and actual data.
Secondly, where are you trying to access this page from? Would it be a child of the current page? If it's the child, you can simply use something like:
{% CurrentDocument.Parent.DocumentName %}
If it's in another node in the content tree, use something like:
{% Documents["/test"].AllChildren.FirstItem.DocumentName %}
Also, DocumentHelper.GetDocuments()
is a C# method and not available using the K# macro engine.