Python time mocking
time-travel - time and I/O mocking library
time-travel is a python library that helps users write deterministic tests for time sensitive and I/O intensive code.
time-travel supports python 2.7, 3.4, 3.5, 3.6 and pypy2 on both Linux and Windows.
$ pip install time_travel
Testing Time Sensitive Code
Imagine testing a state machine that times out after some time passes. One way to test it would be:
def test_state_timeout(): sm.handle_event(event=...) time.sleep(5) sm.handle_event(event=...) assert sm.state == TIMEOUT
This is bad for several reasons:
- Your test takes 5 seconds to run. That’s a no-no.
- time.sleep() promises that the process will sleep x seconds at most. This test might fail randomly, depending on how sensitive your state machine is.
There’s nothing worse than a heisenbuild (well, perhaps a SLOW heisenbuild). Here’s a better way to do this using time-travel:
def test_state_timeout(): with TimeTravel() as tt: sm.handle_event(event=...) tt.clock.time += 5 sm.handle_event(event=...) assert sm.state == TIMEOUT
When the handle_event method is called it will probably check the time using one of time or datetime modules. These modules are patched by time-travel and return the value stored in TimeTravel.clock.time.
From now on, your time sensitive tests will run faster, accurately, and your build will be consistent.
Testing I/O Code
time-travel also mocks I/O event interfaces such as select and poll.
Testing code that uses select is easy - you just inject a real socket object and send data to it from your test code. But what about timeouts? Testing behaviour that occurs on timeout forces you to actually wait! That’s bananas!
Here’s how you’d do it with time-travel:
def test_select_timeout(): with TimeTravel() as tt: sock = socket.socket() tt.add_future_event(2, sock, tt.event_types.select.WRITE) start = time.time() assert select.select([sock], [sock], ) == (, [sock], ) # This will be satisfied after "2 seconds" assert time.time() == start + 2 # You see? 2 seconds! assert select.select([sock], [sock], , 100) == (, , ) # This is the "timeout" assert time.time() == start + 2 + 100
Once again, this code will run instantly.
Oh yes, sock doesn’t even have to be a socket object :)
For detailed information and usage examples, see the full documentation. You know you want to.
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