ipytest - Unit tests in IPython notebooks

Usage | Global state | How does it work? | Changes | Reference | Development | Related packages | License

Sometimes quick experiments in IPython grow large and you find yourself wanting unit tests. This module aims to make testing code in IPython notebooks easy. At its core, it offers a way to run pytest tests inside the notebook environment. It is also designed to make the transfer of the tests into proper python modules easy.

Installation: pip install ipytest

Features:

• support for pytest inside notebooks (with all bells and whistles)
• tight integration with IPython via magics and automatic code transforms

Usage

For usage see the example notebook or the documentation for the core API below. The suggested way to import ipytest is:

import ipytest
ipytest.autoconfig()

Afterwards in a new cell, tests can be executed as in:

%%ipytest -qq

def test_example():
    assert [1, 2, 3] == [1, 2, 3]

This command will first delete any previously defined tests, execute the cell and then run pytest. It is also possible to use ipytest without magics by calling the run function as in:

ipytest.run()

This function is a thin wrapper around pytest.main and will execute any tests defined in the current notebook session. See the reference for a detailed list of available functionality.

NOTE: Some notebook implementations modify the core IPython package and magics may not work correctly (see here or here). In this case, using ipytest.run and ipytest.clean_tests directly should still work as expected.

Global state

There are multiple sources of global state when using pytest inside the notebook:

1. pytest will find any test function ever defined. This behavior can lead to unexpected results when test functions are renamed, as their previous definition is still available inside the kernel. ipytest ships the clean_test function to delete such instances. Also the %%ipytest magic clears any previously defined tests.
2. Python's module system caches imports and therefore acts as a global state. To test the most recent version of any module, the module needs to be reloaded. ipytest offers the reload function. The autoreload extension of IPython may also help here. To test local packages, it is advisable to install them as development packages, e.g., pip install -e ..
3. For async code, IPython will create an event loop in the current thread. This setup may interfere with async tests. To support these use cases, ipytest supports running tests in a separate thread. Simply setup ipytest via ipytest.autoconfig(run_in_thread=True).

How does it work?

In its default configuration (via autoconfig()), ipytest performs the following steps:

1. Register pytest's assertion rewriter with the IPython kernel. The rewriter will rewrite any assert statements entered into the notebook to give better error messages. This change will affect also non test based code, but should generally improve the development experience.
2. Ensure the notebook can be mapped to a file. ipytest will create a temporary file in the current directory and remove if afterwards.
3. Register the notebook scope temporarily as a module. This step is necessary to allow pytest's doctest plugin to import the notebook.
4. Call pytest with the name of the temporary module

ipytest can pass additional arguments to pytest. Per default, only the filename that is associated with the notebook is passed. There are a number of ways to configure this behavior:

• ipytest.config(addopts=...) or ipytest.autconfig(addopts=...) allow to specify a list of strings that are added to the command line. For example, ipytest.autoconfig(addopts=["-x", "--pdb"]) will attach the debugger on the first test failure and not run further tests.
• ipytest.run(...): allows to specify additional arguments as strings
• %%ipytest allows to specify additional arguments in the same line
• ipytest.config(defopts=False) or ipytest.autoconfig(defopts=False) will instruct ipytest to not pass the current module filename. It can still be passed manually by adding {MODULE} to the command line.

The arguments are formatted using Python's standard string formatting. Currently, only the {MODULE} variable is understood. It is replaced with the filename associated with the notebook.

Changes

Note: development is tracked on the develop branch.

• 0.11.0:
  • Overwrite the program name in pytest error messages for incorrect arguments
  • Deprecate %%run_pytest and %%run_pytest[clean] in favor of %%ipytest
  • Force color pytest output by default by adding --color=yes to the default addopts value
  • Configure the number of columns available to pytest
  • Add warning and workaround for non-standard IPython implementations
• 0.10.0:
  • Remove the ModuleCollectorPlugin in favor of relying on pytest's builtin collection mechanism
  • Allow to fully customize the command line and to skip passing the current module as an argument
  • Simplify config implementation: restrict config changes to function calls
  • Allow to use the generated module name in the arguments passed to pytest by using {MODULE}
  • Require python>=3.6
  • Remove %%rewrite_asserts magic
  • Remove tempfile_fallback config option
  • Remove register_module config option
  • Remove raise_on_error config option
  • Remove filename argument for ipytest.run
  • Remove return_exit_code argument from ipytest.run
  • Remove running_as_test function
• 0.9.1:
  • Add ipython as an explicit dependency
• 0.9.0:
  • Add Pytest>=5.4 to the requirements
  • Remove legacy functionality, mostly plain unittest integration
  • The tempfile_fallback also kicks in, if a filename was configured, but the file does not exist
  • Add register_module option to register the notebook with the module system of Python. This way --doctest-modules works as expected
• 0.8.1: release with sdist for conda-forge
• 0.8.0:
  • Add the autoconfig helper to simplfy setup with reasonable defaults
  • Stop using deprecated pytest API
• 0.7.1:
  • fix assertion rewriting for pytest>=5.0.0
• 0.7.0:
  • add option to run tests in separate threads. This change allows to test async code with the pytest_asyncio plugin
  • add a proper signature to ipytest.config(...) and show the current settings as a repr.
• 0.6.0: officially remove python 2 support. While ipytest was marked to work on python 2 and python 3, this statement was not tested and most likely not true. This change only documents the current state.
• 0.5.0:
  • Fix assertion rewriting via magics in ipython>=7
  • Add support to raise a RuntimeError on test errors (set ipytest.config.raise_on_error = True)
  • Add support to set base arguments (set ipytest.config.addopts = [])
  • Add config setting to enable magics (set ipytest.config.magics = True).
  • Add config setting to create a temporary file to work without the notebook filename (set ipytest.config.tempfile_fallback = True).
  • Allow to set multiple config values at the same time by calling the config object (ipytest.config(...)).
  • Add ipytest.running_as_test() to detect whether a notebook is executed as a test.
• 0.4.0: add support for automatic AST transforms, deprecate non pytest API.
• 0.3.0: change default pattern for clean_tests to match pytest discovery
• 0.2.2: add support for assert rewriting with current pytest versions
• 0.2.1: add ipython magics to simplify test execution
• 0.2.0: support for using pytest inside notebooks
• 0.1.0: support for running unittest.FunctionTestCase, unittest.TestCases, and doctests.

Reference

ipytest.autoconfig

ipytest.autoconfig(rewrite_asserts=<default>, magics=<default>, clean=<default>, addopts=<default>, run_in_thread=<default>, defopts=<default>, display_columns=<default>)

Configure ipytest with reasonable defaults.

Specifically, it sets:

• rewrite_asserts: True
• magics: True
• clean: '[Tt]est*'
• addopts: ('-q', '--color=yes')
• run_in_thread: False
• defopts: True
• display_columns: 100

See ipytest.config for details.

%%ipytest ...

IPython magic that first executes the cell, then executes ipytest.run(). Any arguments passed on the magic line be passed on to pytest. It cleans any previously found tests, i.e., only tests defined in the current cell are executed. To disable this behavior, use ipytest.config(clean=False). To register the magics, run ipytest.autoconfig() or ipytest.config(magics=True) first.

Additional arguments can be passed to pytest. See the section "How does it work" for specifics.

For example:

%%ipytest -qq


def test_example():
    ...

ipytest.config

ipytest.config(rewrite_asserts=<keep>, magics=<keep>, clean=<keep>, addopts=<keep>, run_in_thread=<keep>, defopts=<keep>, display_columns=<keep>)

Configure ipytest

To update the configuration, call this function as in:

ipytest.config(rewrite_asserts=True)

The following settings are supported:

• rewrite_asserts (default: False): enable ipython AST transforms globally to rewrite asserts
• magics (default: False): if set to True register the ipytest magics
• clean (default: [Tt]est*): the pattern used to clean variables
• addopts (default: ()): pytest command line arguments to prepend to every pytest invocation. For example setting ipytest.config(addopts=['-qq']) will execute pytest with the least verbosity. Consider adding --color=yes to force color output
• run_in_thread (default: False): if True, pytest will be run a separate thread. This way of running is required when testing async code with pytest_asyncio since it starts a separate event loop
• defopts (default: True): if True, ipytest will add the current module to the arguments passed to pytest. If False only the arguments given and adopts are passed. Such a setup may be helpful to customize the test selection
• display_columns (default: 100) if not False, configure Pytest to use the given number of columns for its output. This option will temporarily override the COLUMNS environment variable.

ipytest.exit_code

The return code of the last pytest invocation.

ipytest.run

ipytest.run(*args, module=None, plugins=())

Execute all tests in the passed module (defaults to main) with pytest.

Parameters

• args (any): additional commandline options passed to pytest
• module (any): the module containing the tests. If not given, main will be used.
• filename (any): the filename of the file containing the tests. It has to be a real file, e.g., a notebook name, since itts existence will be checked by pytest. If not given, the file attribute of the passed module will be used.
• plugins (any): additional plugins passed to pytest.

ipytest.clean_tests

ipytest.clean_tests(pattern='[Tt]est*', items=None)

Delete tests with names matching the given pattern.

In IPython the results of all evaluations are kept in global variables unless explicitly deleted. This behavior implies that when tests are renamed the previous definitions will still be found if not deleted. This method aims to simply this process.

An effecitve pattern is to start with the cell containing tests with a call to clean_tests, then defined all test cases, and finally call run_tests. This way renaming tests works as expected.

Arguments:

• pattern: a glob pattern used to match the tests to delete.
• • items: the globals object containing the tests. If None is given, the: globals object is determined from the call stack.

ipytest.reload

ipytest.reload(*mods)

Reload all modules passed as strings.

This function may be useful, when mixing code in external modules and notebooks.

Usage:

reload("ipytest._util", "ipytest")

Development

Setup the virtual environment via:

pip install -r requirements-dev.txt

To execute the unit tests of ipytest run

python make.py test
python make.py integration

Before commit execute python make.py precommit to update the documentation, format the code, and run tests.

To create a new release execute:

python make.py release

Related packages

ipytest is designed to enable running tests within an interactive notebook session. There are also other packages that aim to use notebooks as tests themselves, for example by comparing the output of running all cells to the output of previous runs. These packages include:

• nbval is actively maintained. It is also used in the integration tests of ipytest.
• pytest-ipynb seems to be no longer maintained as the latest commit was on March 2016. .
• ...

Please create an issue, if I missed a packaged or mischaracterized any package.

License

The MIT License (MIT)
Copyright (c) 2015 - 2021 Christopher Prohm

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