Finding leaking tests with pytest

On one project we had a problem with leaking tests, and problem was so huge that some tests was leaking even for a few GB. We tried pytest-leaks, but it was a bit overkill and didn’t worked with our python version. So we wrote a little leak detector by ourselves.

First of all we got consumed RAM with psutil:

import os
from psutil import Process

_proc = Process(os.getpid())


def get_consumed_ram():
    return _proc.memory_info().rss

Then created some log of ram usage, where nodeid is a special pytest representation of test, like tests/test_service.py::TestRemoteService::test_connection:

from collections import namedtuple

START = 'START'
END = 'END'
ConsumedRamLogEntry = namedtuple('ConsumedRamLogEntry', ('nodeid', 'on', 'consumed_ram'))
consumed_ram_log = []

And logged ram usage from pytest hooks, which we just put in conftest.py:

def pytest_runtest_setup(item):
    log_entry = ConsumedRamLogEntry(item.nodeid, START, get_consumed_ram())
    consumed_ram_log.append(log_entry)


def pytest_runtest_teardown(item):
    log_entry = ConsumedRamLogEntry(item.nodeid, END, get_consumed_ram())
    consumed_ram_log.append(log_entry)

Pytest calls pytest_runtest_setup before each test, and pytest_runtest_teardown after.

And after all tests we print information about tests leaked more than allowed (10MB in our case) from pytest_terminal_summary hook:

from itertools import groupby

LEAK_LIMIT = 10 * 1024 * 1024


def pytest_terminal_summary(terminalreporter):
    grouped = groupby(consumed_ram_log, lambda entry: entry.nodeid)
    for nodeid, (start_entry, end_entry) in grouped:
        leaked = end_entry.consumed_ram - start_entry.consumed_ram
        if leaked > LEAK_LIMIT:
            terminalreporter.write('LEAKED {}MB in {}\n'.format(
                leaked / 1024 / 1024, nodeid))

So after running tests we got our leaking tests, like:

LEAKED 712MB in tests/test_service.py::TestRemoteService::test_connection