Python assert with repeat

Question

I am trying to use pytest to create some sort of automation suite. The product suite I am trying to write around communicates over network interface. I am using assert statements like

assert A == B

The main issue I want to address is this:

B takes different amounts of time to reach the desired value (e.g.: sometimes 2 seconds, sometimes 5 seconds)

Is it possible to implement an assert statement which kind of executes the given condition for a certain number of times with a delay and then assert?

assert A == B, 5, 5.0, "Still it failed"

The above statement would mean: "try A == B 5 times with 5.0 second delay between each iteration and after that emit given error if it still fails."

loop over range(5), try the assert, sleep 5 seconds would be one naive way... — Jon Clements
– Jon Clements, Commented Sep 7, 2018 at 18:27

Sunitha · Accepted Answer · 2018-09-07 20:37:10Z

4

For a better and more readable code, you can use the retry decorator on a inner function. Do pip install retry to install the retry module

from retry import retry

def test_abc():
    # <my test code>

    @retry(AssertionError, tries=5, delay=5.0)
    def _check_something():
        assert A == B, "Still failing even after 5 tries"

    # Validate
    _check_something()

edited Sep 7, 2018 at 20:37

answered Sep 7, 2018 at 19:03

Sunitha

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Comments

Prune · Accepted Answer · 2018-09-07 18:28:54Z

3

No, but you can write a loop that does the same thing.

import time
failed = True
i = 0

while i < 5 and failed:
    failed = (A == B)
    time.sleep(5.0)

assert not failed, "Still it failed"

Wrap that into a function for readability ...

answered Sep 7, 2018 at 18:28

Prune

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4 Comments

vk-code Over a year ago

I have something similar written, I wanted to have a compact version of above loop because as you can see in above code only (A == B) changes for different conditions but rest of the code is same, unnecessarily makes the code redundant and big

Prune Over a year ago

Good idea; I left the logic "exploded" for understanding.

lng Over a year ago

I think it should be failed = (A != B), isn't it?

user7610 Over a year ago

@LongNguyen depends on what you actually consider a success in your specific case ;P

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