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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-05-04 17:35:20 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-05-04 17:35:20 +0000 |
commit | e106bf94eff07d9a59771d9ccc4406421e18ab64 (patch) | |
tree | edb6545500e39df9c67aa918a6125bffc8ec1aee /docs/pages/advanced_topics/unit_testing.rst | |
parent | Initial commit. (diff) | |
download | prompt-toolkit-e106bf94eff07d9a59771d9ccc4406421e18ab64.tar.xz prompt-toolkit-e106bf94eff07d9a59771d9ccc4406421e18ab64.zip |
Adding upstream version 3.0.36.upstream/3.0.36upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to '')
-rw-r--r-- | docs/pages/advanced_topics/unit_testing.rst | 125 |
1 files changed, 125 insertions, 0 deletions
diff --git a/docs/pages/advanced_topics/unit_testing.rst b/docs/pages/advanced_topics/unit_testing.rst new file mode 100644 index 0000000..01498c9 --- /dev/null +++ b/docs/pages/advanced_topics/unit_testing.rst @@ -0,0 +1,125 @@ +.. _unit_testing: + +Unit testing +============ + +Testing user interfaces is not always obvious. Here are a few tricks for +testing prompt_toolkit applications. + + +`PosixPipeInput` and `DummyOutput` +---------------------------------- + +During the creation of a prompt_toolkit +:class:`~prompt_toolkit.application.Application`, we can specify what input and +output device to be used. By default, these are output objects that correspond +with `sys.stdin` and `sys.stdout`. In unit tests however, we want to replace +these. + +- For the input, we want a "pipe input". This is an input device, in which we + can programatically send some input. It can be created with + :func:`~prompt_toolkit.input.create_pipe_input`, and that return either a + :class:`~prompt_toolkit.input.posix_pipe.PosixPipeInput` or a + :class:`~prompt_toolkit.input.win32_pipe.Win32PipeInput` depending on the + platform. +- For the output, we want a :class:`~prompt_toolkit.output.DummyOutput`. This is + an output device that doesn't render anything. We don't want to render + anything to `sys.stdout` in the unit tests. + +.. note:: + + Typically, we don't want to test the bytes that are written to + `sys.stdout`, because these can change any time when the rendering + algorithm changes, and are not so meaningful anyway. Instead, we want to + test the return value from the + :class:`~prompt_toolkit.application.Application` or test how data + structures (like text buffers) change over time. + +So we programmatically feed some input to the input pipe, have the key +bindings process the input and then test what comes out of it. + +In the following example we use a +:class:`~prompt_toolkit.shortcuts.PromptSession`, but the same works for any +:class:`~prompt_toolkit.application.Application`. + +.. code:: python + + from prompt_toolkit.shortcuts import PromptSession + from prompt_toolkit.input import create_pipe_input + from prompt_toolkit.output import DummyOutput + + def test_prompt_session(): + with create_pipe_input() as inp: + inp.send_text("hello\n") + session = PromptSession( + input=inp, + output=DummyOutput(), + ) + + result = session.prompt() + + assert result == "hello" + +In the above example, don't forget to send the `\\n` character to accept the +prompt, otherwise the :class:`~prompt_toolkit.application.Application` will +wait forever for some more input to receive. + +Using an :class:`~prompt_toolkit.application.current.AppSession` +---------------------------------------------------------------- + +Sometimes it's not convenient to pass input or output objects to the +:class:`~prompt_toolkit.application.Application`, and in some situations it's +not even possible at all. +This happens when these parameters are not passed down the call stack, through +all function calls. + +An easy way to specify which input/output to use for all applications, is by +creating an :class:`~prompt_toolkit.application.current.AppSession` with this +input/output and running all code in that +:class:`~prompt_toolkit.application.current.AppSession`. This way, we don't +need to inject it into every :class:`~prompt_toolkit.application.Application` +or :func:`~prompt_toolkit.shortcuts.print_formatted_text` call. + +Here is an example where we use +:func:`~prompt_toolkit.application.create_app_session`: + +.. code:: python + + from prompt_toolkit.application import create_app_session + from prompt_toolkit.shortcuts import print_formatted_text + from prompt_toolkit.output import DummyOutput + + def test_something(): + with create_app_session(output=DummyOutput()): + ... + print_formatted_text('Hello world') + ... + +Pytest fixtures +--------------- + +In order to get rid of the boilerplate of creating the input, the +:class:`~prompt_toolkit.output.DummyOutput`, and the +:class:`~prompt_toolkit.application.current.AppSession`, we create a +single fixture that does it for every test. Something like this: + +.. code:: python + + import pytest + from prompt_toolkit.application import create_app_session + from prompt_toolkit.input import create_pipe_input + from prompt_toolkit.output import DummyOutput + + @pytest.fixture(autouse=True, scope="function") + def mock_input(): + with create_pipe_input() as pipe_input: + with create_app_session(input=pipe_input, output=DummyOutput()): + yield pipe_input + + +Type checking +------------- + +Prompt_toolkit 3.0 is fully type annotated. This means that if a +prompt_toolkit application is typed too, it can be verified with mypy. This is +complementary to unit tests, but also great for testing for correctness. |