How do I know when I am "fluent"? What in a common test for fluency in Chinese?

Is it when I can;


talk to a shopkeeper
converse meaningfully about a film
do business purely in Chinese
pass HSK6


When my friends ask I don't know what to say.
Here's my two cents. 

Out of those four choices you provided us, I'd say that conversing meaningfully about a film (or a book or a painting) and conducting business strictly in Chinese are very close to fluency.

Also, being fluent in a language does not pinpoint at a clear-cut level. You can be "just" fluent and be fluent like a native speaker. There's usually a difference between the two. Moreover, different native speakers elicit different levels of fluency. Compare a five year-old child with a novelist. Both are fluent, but one of them has a greater command of the language and a greater ability to convey his ideas with clarity and succinctness. 

In the end, it all comes down to what you're happy with and what your aspirations are. When things start clicking in real-time, you are almost there. But, even after you reach fluency, you may still have a long path to go. 

Finally, your mother language plays an important role in how fast you can become fluent and continue to make progress after you have reached that level. I'm not talking about Chinese here, but about any language in general.