Check if unassigned variable exists in Request.QueryString

Question

Within the context of an ASP.NET page, I can use Request.QueryString to get a collection of the key/value pairs in the query string portion of the URI.

For example, if I

Answer 1

Request.QueryString.ToString().Contains("test")

This works in the special case where you're looking for a single querystring parameter, e.g. MyFile.aspx?test

For more complex, general, cases then other solutions would be better.