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Locust ep 5: How to use test_start and test_stop Events in Locust
21 November 2024 at 04:30
Locust provides powerful event hooks, such as test_start and test_stop, to execute custom logic before and after a load test begins or ends. These events allow you to implement setup and teardown operations at the test level, which applies to the entire test run rather than individual users.
In this blog, we will
- Understand what
test_startandtest_stopare. - Explore their use cases.
- Provide examples of implementing these events.
- Discuss how to run and validate the setup.
What Are test_start and test_stop?
test_start: Triggered when the test starts. Use this event to perform actions like initializing global resources, starting external systems, or logging test start information.test_stop: Triggered when the test ends. This event is ideal for cleanup operations, aggregating results, or stopping external systems.
These events are global and apply to the entire test environment rather than individual user instances.
Why Use test_start and test_stop?
- Global Setup: Initialize shared resources, like database connections or external services.
- Logging: Record timestamps or test details for audit or reporting purposes.
- External System Management: Start/stop services that the test depends on, such as mock servers or third-party APIs.
Example: Basic Usage of test_start and test_stop
Here’s a basic example demonstrating the usage of these events
from locust import User, task, between, events
from datetime import datetime
# Global setup: Perform actions at test start
@events.test_start.add_listener
def on_test_start(environment, **kwargs):
print("Test started at:", datetime.now())
# Global teardown: Perform actions at test stop
@events.test_stop.add_listener
def on_test_stop(environment, **kwargs):
print("Test stopped at:", datetime.now())
# Simulated user behavior
class MyUser(User):
wait_time = between(1, 5)
@task
def print_datetime(self):
"""Task that prints the current datetime."""
print("Current datetime:", datetime.now())
Running the Example
- Save the code as
locustfile.py. - Start Locust -> `
locust -f locustfile.py` - Configure the test parameters (number of users, spawn rate, etc.) in the web UI at http://localhost:8089.
- Observe the console output:
- A message when the test starts (
on_test_start). - Messages during the test as users execute tasks.
- A message when the test stops (
on_test_stop).
- A message when the test starts (
Example: Logging Test Details
You can log detailed test information, like the number of users and host under test, using environment and kwargs
from locust import User, task, between, events
@events.test_start.add_listener
def on_test_start(environment, **kwargs):
print("Test started!")
print(f"Target host: {environment.host}")
print(f"Total users: {environment.runner.target_user_count}")
@events.test_stop.add_listener
def on_test_stop(environment, **kwargs):
print("Test finished!")
print("Summary:")
print(f"Requests completed: {environment.stats.total.num_requests}")
print(f"Failures: {environment.stats.total.num_failures}")
class MyUser(User):
wait_time = between(1, 5)
@task
def dummy_task(self):
pass
Observing the Results
When you run the above examples
- At Test Start: Look for messages indicating setup actions, like initializing external systems or printing start time.
- During the Test: Observe user tasks being executed.
- At Test Stop: Verify that cleanup actions were executed successfully.
