One of the first things I always find myself doing when writing an application using the Google Visualization API Query Language is writing a simple application framework to test out my data models and queries. Rather than re-inventing the wheel on every project, I decided to just implement a simple tester here where, hopefully, everyone else can benefit from it as well.
To use it, simply place the datasource URL you intend to use as well as the query string in the appropriate blanks below. Then click, 'Test Query' to see the results of the query. For example, you can try the datasource URL and a query string from the Hierarchical Chooser post.
datasource URL: http://spreadsheets.google.com/pub?key=pvFXGB-79Kl2d6jU-_m44ZQ&gid=0&pub=1
Query String: Select A, B, C