Testing Asphalt components¶
Testing Asphalt components and component hierarchies is a relatively simple procedure:
- Create an instance of your
- Create a
- Run the component’s
start()method with the context as the argument
- Run the tests
- Close the context to release any resources
With Asphalt projects, it is recommended to use the py.test testing framework because it is already being used with Asphalt core and it provides easy testing of asynchronous code (via the pytest-asyncio plugin).
Let’s build a test suite for the Echo Tutorial.
The client and server components could be tested separately, but to make things easier, we’ll test them against each other.
tests directory at the root of the project directory and create a module named
test_client_server there (the
test_ prefix is important):
import asyncio import pytest from asphalt.core import Context from echo.client import ClientComponent from echo.server import ServerComponent @pytest.fixture def event_loop(): # Required on pytest-asyncio v0.4.0 and newer since the event_loop fixture provided by the # plugin no longer sets the global event loop loop = asyncio.new_event_loop() asyncio.set_event_loop(loop) yield loop loop.close() @pytest.fixture def context(event_loop): with Context() as ctx: yield ctx @pytest.fixture def server_component(event_loop, context): component = ServerComponent() event_loop.run_until_complete(component.start(context)) def test_client(event_loop, server_component, context, capsys): client = ClientComponent('Hello!') event_loop.run_until_complete(client.start(context)) exc = pytest.raises(SystemExit, event_loop.run_forever) assert exc.value.code == 0 # Grab the captured output of sys.stdout and sys.stderr from the capsys fixture out, err = capsys.readouterr() assert out == 'Message from client: Hello!\nServer responded: Hello!\n'
The test module above contains one test function (
test_client) and three fixtures:
event_loop: provides an asyncio event loop and closes it after the test
contextprovides the root context and runs teardown callbacks after the test
server_component: creates and starts the server component
The client component is not provided as a fixture because, as always with
CLIApplicationComponent, starting it would run the logic we want
to test, so we defer that to the actual test code.
In the test function (
test_client), the client component is instantiated and started. Since the
start() function only kicks off the task that runs the client’s business logic (the
run() method), we have to wait until the task is complete by running the event loop (using
run() finishes and its callback code
attempts to terminate the application. For that purpose, we catch the resulting
exception and verify that the application indeed completed successfully, as indicated by the return
code of 0.
Finally, we check that the server and the client printed the messages they were supposed to.
When the server receives a line from the client, it prints a message to standard output using
print(). Likewise, when the client gets a response from the server, it too prints out its
own message. By using pytest’s built-in
capsys fixture, we can capture the output and verify it
against the expected lines.
To run the test suite, make sure you’re in the project directory and then do:
For more elaborate examples, please see the test suites of various Asphalt subprojects.