I want to make sure that in case the code is running in test mode, that it does not (accidentally) access the wrong database. What is the best way to detect if the code is currently running in test mode?
As already mentioned in comment it is bad practice to build your code aware of tests. I even can't find mentioned topic on SO and even outside.
However, I can think of ways to detect the fact of being launched in test.
For me mocha doesn't add itself to global scope, but adds global.it.
So your check may be
var isInTest = typeof global.it === 'function';
I would suggest to be sure you don't false-detect to add check for global.sinon and global.chai which you most likely used in your node.js tests.