Many applications rely on datetime.datetime.now() to create a timestamp. When we use this with a unit test, the results are essentially impossible to predict. We have a dependency injection problem here, our application depends on a class that we would like to replace only when we're testing.
One option is to avoid now() and utcnow(). Instead of using these directly, we can create a factory function that emits timestamps. For test purposes, this function can be replaced with one that produces known results. It seems awkward to avoid using the now() method in a complex application.
Another option is to avoid direct use of the datetime class entirely. This requires designing classes and modules that wrap the datetime class. A wrapper class that produces known values for now() can then be used for testing. This, too, seems needlessly...
