pyodide/docs/development/testing.md

(testing)=
# Testing and benchmarking

## Testing

### Requirements

Install the following dependencies into the default Python installation:

```bash
pip install pytest selenium pytest-instafail pytest-httpserver
```

Install [geckodriver](https://github.com/mozilla/geckodriver/releases) and
[chromedriver](https://sites.google.com/a/chromium.org/chromedriver/downloads)
and check that they are in your `PATH`.

### Running the test suite

To run the pytest suite of tests, type on the command line:

```bash
pytest src/ pyodide_build/ packages/*/test_*
```

There are 3 test locations,
- `src/tests/`: general pyodide tests and tests running the CPython test suite
- `pyodide_build/tests/`: tests related to pyodide build system (do not require selenium to run)
- `packages/*/test_*`: package specific tests.

### Manual interactive testing

To run manual interactive tests, a docker environment and a webserver will be
used.

1. Bind port 8000 for testing. To automatically bind port 8000 of the docker
environment and the host system, run: `./run_docker`

2. Now, this can be used to test the `pyodide` builds running within the
docker environment using external browser programs on the host system. To do
this, run: `./bin/pyodide serve`

3. This serves the ``build`` directory of the ``pyodide`` project on port 8000.
    * To serve a different directory, use the ``--build_dir`` argument followed
      by the path of the directory.
    * To serve on a different port, use the ``--port`` argument followed by the
      desired port number. Make sure that the port passed in ``--port`` argument
      is same as the one defined as ``DOCKER_PORT`` in the ``run_docker`` script.


4. Once the webserver is running, simple interactive testing can be run by
   visiting this URL:
   [http://localhost:8000/console.html](http://localhost:8000/console.html)

## Benchmarking

To run common benchmarks to understand Pyodide's performance, begin by
installing the same prerequisites as for testing. Then run:

```bash
make benchmark
```

## Linting

Python is linted with `flake8`.  C and Javascript are linted with
`clang-format`.

To lint the code, run:

```bash
make lint
```

## Testing framework

### run_in_pyodide
Many tests simply involve running a chunk of code in pyodide and ensuring it
doesn't error. In this case, one can use the `run_in_pyodide` decorate from
`pyodide_build/testing.py`, e.g.

```python
from pyodide_build.testing import run_in_pyodide

@run_in_pyodide
def test_add():
    assert 1 + 1 == 2
```
In this case, the body of the function will automatically be run in pyodide.
The decorator can also be called with arguments. It has two configuration
options --- standalone and packages.

Setting `standalone = True` starts a standalone browser session to run the test
(the session is shared between tests by default). This is useful for testing
things like package loading.

The `packages` option lists packages to load before running the test. For
example,
```python
from pyodide_build.testing import run_in_pyodide

@run_in_pyodide(standalone = True, packages = ["regex"])
def test_regex():
    import regex
    assert regex.search("o", "foo").end() == 2
```