Fix for time based mongodb test

[ranbena]

What type of PR is this?

• Bug Fix

Description

The following is flaky since if a second passes between the two time dependent commands, the test fails as it did here resulting in:

=================================== FAILURES ===================================
_____________ TestParseQueryJson.test_supports_relative_timestamps _____________

self = <tests.query_runner.test_mongodb.TestParseQueryJson testMethod=test_supports_relative_timestamps>

    def test_supports_relative_timestamps(self):
        query = {
            'ts': {'$humanTime': '1 hour ago'}
        }
    
        one_hour_ago = parse_human_time("1 hour ago")
        query_data = parse_query_json(json_dumps(query))
>       self.assertEqual(query_data['ts'], one_hour_ago)
E       AssertionError: datetime.datetime(2019, 3, 21, 9, 24, 12) != datetime.datetime(2019, 3, 21, 9, 24, 11)

Reproduce

Insert a 2 second sleep.

one_hour_ago = parse_human_time("1 hour ago")
time.sleep(2) # <-- 2s delay
query_data = parse_query_json(json_dumps(query))
self.assertEqual(query_data['ts'], one_hour_ago) # <-- fails due to 2s delta

The fix

Mock "now()" with freezegun.

@freeze_time('2019-01-01 12:00:00')
def test_supports_relative_timestamps(self):
    query = {
        'ts': {'$humanTime': '1 hour ago'}
    }

    one_hour_ago = parse_human_time("1 hour ago")
    time.sleep(2) # <-- 2s delay
    query_data = parse_query_json(json_dumps(query))
    self.assertEqual(query_data['ts'], one_hour_ago) # <-- passes