How do I repeat a python PyTest multiple times, utilizing values carried over from the previous test

Question

I'm trying to create a test which involves sending data to an external piece of hardware, rebooting that hardware, and asserting whether the hardware's data matches what was previously sent. This will be repeated 1000's of times, ultimately.

So the steps look like this:

Query hardware for current running ID (the beforementioned data)
Compare and assert it's still the same as id that was previously sent (or in the first test "id = 1)
Create a new id (id += 1), save it somewhere, and then send it to the hardware.
Repeat.

My question is how do I carry over this saved "id" between tests to compare? I was going to just read/write from a json as I've seen many people saying global variables are bad, but I'm not sure saving to a json is the best option.

JSON or DB would be the options to choose from. JSON file does seem better. — Devang Sanghani
– Devang Sanghani, Commented Feb 4, 2022 at 8:15
As long as you know what you are doing with a global variable, it should be fine. In the end, it's there for a reason. — BcK
– BcK, Commented Feb 4, 2022 at 8:25

Roland Smith · Accepted Answer · 2022-02-04 10:54:35Z

5

One thing you could do is run a for-loop in the test.

def test_hardware():
    previous_id = 1
    set_hardware_id(1)
    for i in range(2, 100):
        current_id = get_hardware_id()
        # this fill fail at the first mismatch
        assert current_id == previous_id
        previous_id = current_id
        set_hardware_id(i)

If you want to run the whole test itself repeatedly, use the @pytest.mark.parametrize decorator.

@pytest.mark.parametrize("test_input", range(100))
def test_hardware(test_input):
    set_hardware_id(test_input)
    result = get_hardware_id()
    assert result == test_input

edited Feb 4, 2022 at 10:54

answered Feb 4, 2022 at 8:42

Roland Smith

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2 Comments

Steven Teglman Over a year ago

Thank you for you suggestion. I was more hoping to start a new test for each iteration.

Roland Smith Over a year ago

@StevenTeglman See updated answer.

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