Pytest

The Pytest module runs your Python tests with Pytest, the same way locally, in CI, and in Dagger Cloud. Python projects and their test files are collections, so a check can run one project, one test file, or everything. It can use a custom Python container when the default environment is not enough.

Add it to your workspace

dagger module install dagger.io/python/pytest

Run the tests

dagger check --pytest                                                # run every project
dagger check --pytest-project=svc                                    # run one project
dagger check --pytest-project=svc --pytest-test-file=tests/test_add.py   # run one test file

The check is pytest/projects/tests/test. It runs once per project, over the selected test files. With every file in the project selected, it runs pytest on the whole project. With some selected, it runs only those files. A check over several projects reports every project that fails.

The module injects pytest_otel automatically, so individual Python tests appear as spans in the Dagger TUI and Dagger Cloud with no project changes. The module uses uv to install the project dependencies, pytest, and pytest_otel together.

Collections

Flag	Collection	Key
--pytest-project	projects	Project root, relative to the workspace root. The root is .
--pytest-test-file	tests, on a project	Test file path, relative to the project

List the keys with dagger list pytest-projects -a and dagger list pytest-test-files -a. Select collection items describes how to select items.

A project is a directory holding pytest.ini, pyproject.toml, tox.ini, or setup.cfg, with at least one test file of its own. A test file is named test_*.py or *_test.py and defines a test function or a Test class. A file belongs to the deepest project that contains it. A uv workspace member or path source inside the project that declares it is tested with that project.

Projects are found at or below the directory dagger runs from, plus the nearest project that encloses it. Virtual environments, site-packages, node_modules, and caches are left out.

Configure it

List the current settings and their values with dagger module settings pytest, then set one with dagger module settings pytest <key> <value>. Settings are stored in dagger.toml under [modules.pytest.settings] and apply to every project:

• version (default 3.14) is the Python version the default container provisions, such as 3.13 or 3.12. It cannot be combined with a custom base.
• base (default: none) is a custom container that already has Python and uv installed. Set it when tests need system packages, a private index, or other tools.
• args (default ["-v"]) are arguments passed straight to pytest, such as ["-x", "--tb=short"].
• scope (default ["**"]) selects project roots to test, as paths from the workspace root. A bare pattern selects, a !-prefixed pattern excludes, and an exclusion always wins whatever the order, so ["**", "!docs"] tests everything but docs. A project outside the scope is still listed, and has no test files to run.
• defaultVersion (default 9.1.1) is the pytest version for a project that does not pin its own.
• tracing (default true) loads the bundled OpenTelemetry plugin.
• nesting (default true) lets tests talk to a nested Dagger engine. Turn it off for untrusted test code.

[modules.pytest.settings]
scope = ["**", "!docs"]
args = ["-x", "--tb=short"]

Working with other modules

This module is a good first check for Python repos. Keep it focused on tests; use separate modules for formatting, linting, shell scripts, or generated files.

source code