Shared expensive resource patterns in PyTest - Test Execution Trace

Test Overview

This test demonstrates how to use a shared expensive resource in pytest using a fixture with module scope. It verifies that the resource is created once and reused across multiple tests.

Test Code - pytest

PyTest

import pytest

@pytest.fixture(scope="module")
def expensive_resource():
    print("Setting up expensive resource")
    resource = {"data": [1, 2, 3]}
    yield resource
    print("Tearing down expensive resource")


def test_resource_usage_1(expensive_resource):
    assert expensive_resource["data"] == [1, 2, 3]


def test_resource_usage_2(expensive_resource):
    assert sum(expensive_resource["data"]) == 6

Execution Trace - 5 Steps

Step	Action	System State	Assertion	Result
1	Test runner starts and discovers tests	pytest ready to run tests test_resource_usage_1 and test_resource_usage_2	-	PASS
2	Setup fixture 'expensive_resource' before first test	Prints 'Setting up expensive resource', resource dictionary created	-	PASS
3	Run test_resource_usage_1 using shared resource	Test accesses resource data [1, 2, 3]	Assert resource data equals [1, 2, 3]	PASS
4	Run test_resource_usage_2 using same shared resource	Test accesses resource data [1, 2, 3]	Assert sum of resource data equals 6	PASS
5	Teardown fixture 'expensive_resource' after all tests in module	Prints 'Tearing down expensive resource'	-	PASS

Failure Scenario

Failing Condition: Fixture setup fails or resource data is incorrect

Execution Trace Quiz - 3 Questions

When is the 'expensive_resource' fixture set up in this test pattern?

A Before each test function

B Once before all tests in the module

C After each test function

D Only if a test fails

Key Result

Using a fixture with module scope allows sharing an expensive resource setup once for multiple tests, improving test speed and resource management.