February 2nd, 2017

Vladimir Iakolev: Finding leaking tests with pytest

Programing, Python, by admin.

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'
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

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

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