Allow running sanity and unit tests with antsibull-nox; impove testing documentation

CONTRIBUTING.md

@@ -44,7 +44,49 @@ If you want to test a PR locally, refer to [our testing guide](https://github.co
 
 If you find any inconsistencies or places in this document which can be improved, feel free to raise an issue or pull request to fix it.
 
-## Run sanity, unit or integration tests locally
+## Run sanity or unit locally (with antsibull-nox)
+
+The easiest way to run sanity and unit tests locally is to use [antsibull-nox](https://ansible.readthedocs.io/projects/antsibull-nox/).
+(If you have [nox](https://nox.thea.codes/en/stable/) installed, it will automatically install antsibull-nox in a virtual environment for you.)
+
+### Sanity tests
+
+The following commands show how to run ansible-test sanity tests:
+
+```.bash
+# Run basic sanity tests for all files in the collection:
+nox -Re ansible-test-sanity-devel
+
+# Run basic sanity tests for the given files and directories:
+nox -Re ansible-test-sanity-devel -- plugins/modules/system/pids.py tests/integration/targets/pids/
+
+# Run all other sanity tests for all files in the collection:
+nox -R
+```
+
+If you replace `-Re` with `-e`, respectively. leave `-R` away, then the virtual environments will be re-created. The `-R` re-uses them (if they already exist).
+
+### Unit tests
+
+The following commands show how to run unit tests:
+
+```.bash
+# Run all unit tests:
+nox -Re ansible-test-units-devel
+
+# Run all unit tests for one Python version (a lot faster):
+nox -Re ansible-test-units-devel -- --python 3.13
+
+# Run a specific unit test (for the nmcli module) for one Python version:
+nox -Re ansible-test-units-devel -- --python 3.13 tests/unit/plugins/modules/net_tools/test_nmcli.py
+```
+
+If you replace `-Re` with `-e`, then the virtual environments will be re-created. The `-R` re-uses them (if they already exist).
+
+## Run basic sanity, unit or integration tests locally (with ansible-test)
+
+Instead of using antsibull-nox, you can also run sanity and unit tests with ansible-test directly.
+This also allows you to run integration tests.
 
 You have to check out the repository into a specific path structure to be able to run `ansible-test`. The path to the git checkout must end with `.../ansible_collections/community/general`. Please see [our testing guide](https://github.com/ansible/community-docs/blob/main/test_pr_locally_guide.rst) for instructions on how to check out the repository into a correct path structure. The short version of these instructions is:
 
@@ -56,20 +98,27 @@ cd ~/dev/ansible_collections/community/general
 
 Then you can run `ansible-test` (which is a part of [ansible-core](https://pypi.org/project/ansible-core/)) inside the checkout. The following example commands expect that you have installed Docker or Podman. Note that Podman has only been supported by more recent ansible-core releases. If you are using Docker, the following will work with Ansible 2.9+.
 
-### Sanity tests
+### Basic sanity tests
 
-The following commands show how to run sanity tests:
+The following commands show how to run basic sanity tests:
 
 ```.bash
-# Run sanity tests for all files in the collection:
+# Run basic sanity tests for all files in the collection:
 ansible-test sanity --docker -v
 
-# Run sanity tests for the given files and directories:
+# Run basic sanity tests for the given files and directories:
 ansible-test sanity --docker -v plugins/modules/system/pids.py tests/integration/targets/pids/
 ```
 
 ### Unit tests
 
+Note that for running unit tests, you need to install required collections in the same folder structure that `community.general` is checked out in.
+Right now, you need to install [`community.internal_test_tools`](https://github.com/ansible-collections/community.internal_test_tools).
+If you want to use the latest version from GitHub, you can run:
+```
+git clone https://github.com/ansible-collections/community.internal_test_tools.git ~/dev/ansible_collections/community/internal_test_tools
+```
+
 The following commands show how to run unit tests:
 
 ```.bash
@@ -85,15 +134,25 @@ ansible-test units --docker -v --python 3.8 tests/unit/plugins/modules/net_tools
 
 ### Integration tests
 
+Note that for running integration tests, you need to install required collections in the same folder structure that `community.general` is checked out in.
+Right now, depending on the test, you need to install [`ansible.posix`](https://github.com/ansible-collections/ansible.posix), [`community.crypto`](https://github.com/ansible-collections/community.crypto), and [`community.docker`](https://github.com/ansible-collections/community.docker):
+If you want to use the latest versions from GitHub, you can run:
+```
+mkdir -p ~/dev/ansible_collections/ansible
+git clone https://github.com/ansible-collections/ansible.posix.git ~/dev/ansible_collections/ansible/posix
+git clone https://github.com/ansible-collections/community.crypto.git ~/dev/ansible_collections/community/crypto
+git clone https://github.com/ansible-collections/community.docker.git ~/dev/ansible_collections/community/docker
+```
+
 The following commands show how to run integration tests:
 
 #### In Docker
 
 Integration tests on Docker have the following parameters:
 - `image_name` (required): The name of the Docker image. To get the list of supported Docker images, run
   `ansible-test integration --help` and look for _target docker images_.
-- `test_name` (optional): The name of the integration test.  
-  For modules, this equals the short name of the module; for example, `pacman` in case of `community.general.pacman`.  
+- `test_name` (optional): The name of the integration test.
+  For modules, this equals the short name of the module; for example, `pacman` in case of `community.general.pacman`.
   For plugins, the plugin type is added before the plugin's short name, for example `callback_yaml` for the `community.general.yaml` callback.
 ```.bash
 # Test all plugins/modules on fedora40

antsibull-nox.toml

@@ -46,3 +46,9 @@ doc_fragment = "community.general.proxmox.actiongroup_proxmox"
 
 [sessions.build_import_check]
 run_galaxy_importer = true
+
+[sessions.ansible_test_sanity]
+include_devel = true
+
+[sessions.ansible_test_units]
+include_devel = true