How to test the market for a startup before writing code?

Research I guess. But really, software is one of those things that you write, test, and throwaway all the damn time.

Even if the code is good, the message or the implementation for how people use it could still be crap.

Write some code!

Reach out to your target audience (the paying companies) and see if you can get a couple of them to pay even before you have written any code. If they pay, you have a winner.

Use a modern WYSIWYG -- SquareSpace? -- and drop in KISSmetrics and GoSquared.

But honestly, a startup is just as much about the team and the development of the iterative product w/r/t the given market. Certain products need to take a certain amount of time for the given market to consider it viable, like security software... That's what software maturity and versioning is all about.