Update TESTING guide

Signed-off-by: Webster Mudge <wmudge@cloudera.com>

Author: wmudge

TESTING.md

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+# Testing cloudera.cluster
+
+This project uses [Hatch](https://hatch.pypa.io/dev/) to manage the project dependencies, testing environments, common utilities and scripts, and other activities. It also makes heavy use of [pytest](https://pytest.org).  We also use [pre-commit](https://pre-commit.com/), [antsibull-docs](https://ansible.readthedocs.io/projects/antsibull-docs/), and [ansible-lint](https://ansible.readthedocs.io/projects/lint/) for linting and hygiene.
+
+To set up a development and test environment for the collection, you need to:
+
+1. Set up the Hatch build system
+1. Set up the Ansible Collection and Role paths
+1. Configure the PYTHONPATH to use the correct location of the collections code
+
+## Hatch Build System
+
+You should install `hatch` as [per its documentation](https://hatch.pypa.io/dev/install/#installers). `hatch` should be able to handle all dependencies, including Python versions and virtual environments.
+
+> [!danger] OSX `dirs.data` default!
+> The [default data directory](https://hatch.pypa.io/1.13/config/hatch/#data) for `hatch` is `~/Library/Application Support/hatch`, which causes trouble for `molecule`! You might need to change this location to a path with spaces!
+
+## Ansible Collection and Role Paths
+
+You have to install your Ansible collections, both the collection under test and its dependencies, into the `ansible_collections/<namespace>/<name>` folder structure.  For the collection under test, run the following _in the parent directory of your choosing_:
+
+```bash
+git clone https://github.com/cloudera-labs/cloudera.cluster.git ansible_collections/cloudera/cluster
+```
+
+Then create the `roles` directory in this _parent directory_:
+
+```bash
+mkdir roles
+```
+
+Lastly, set the Ansible [COLLECTION](https://docs.ansible.com/ansible/latest/reference_appendices/config.html#envvar-ANSIBLE_COLLECTIONS_PATH) and [ROLE](https://docs.ansible.com/ansible/latest/reference_appendices/config.html#envvar-ANSIBLE_ROLES_PATH) configurations for these two locations:
+
+```bash
+export ANSIBLE_COLLECTIONS_PATH=$(pwd)
+export ANSIBLE_ROLES_PATH="$(pwd)/roles"
+```
+
+## PYTHONPATH
+
+Make sure to include the `ANSIBLE_COLLECTIONS_PATH` variable to the `PYTHONPATH` to allow module imports.
+
+```bash
+export PYTHONPATH="${ANSIBLE_COLLECTIONS_PATH}":"${PYTHONPATH}"
+```
+
+# Linting and Commits
+
+The `pre-commit` Python application is used to manage linting and other housekeeping functions. The application is installed as a `git` hook and as a Github workflow check.
+
+Commits and pull requests will fail if your contributions do not pass the `pre-commit` checks.  You can check your work-in-progress code by running the following:
+
+```bash
+hatch run lint
+```
+
+Or manually:
+
+```bash
+pre-commit run -a
+```
+
+# pytest Testing
+
+> [!warning] Integration test instructions
+> The vast majority of tests require an existing Cloudera on premise deployment as the target. Currently, these instructions are not yet complete!
+
+To see what tests (unit and integration) are available, run the following from the `ANSIBLE_COLLECTIONS_PATH` directory:
+
+```bash
+pushd ${ANSIBLE_COLLECTIONS_PATH};
+pytest ansible_collections/cloudera/cluster --collect-only;
+popd;
+```
+
+You should see something like:
+
+```
+platform darwin -- Python 3.12.8, pytest-8.4.1, pluggy-1.6.0
+rootdir: /Users/wmudge/Devel/collections/ansible_collections/cloudera/cluster
+configfile: pyproject.toml
+plugins: mock-3.14.1
+collected 475 items
+
+<Dir cluster>
+  <Dir tests>
+    <Package unit>
+      <Dir plugins>
+        <Dir actions>
+          <Dir assemble_cluster_template>
+            <Module test_assemble_cluster_template_action.py>
+              <Function test_empty_parameters>
+              <Function test_missing_src>
+              <Function test_missing_dest>
+              <Function test_remote_src>
+              <Function test_src_not_found>
+              <Function test_src_not_directory>
+              <Function test_invalid_regexp>
+              <Function test_assemble_fragments>
+              <Function test_assemble_fragments_regexp>
+              <Function test_assemble_fragments_malformed>
+        <Dir modules>
+          <Dir assemble_cluster_template>
+            <Module test_assemble_cluster_template_module.py>
+              <Function test_missing_required>
+              <Function test_missing_dest>
+```
+
+To run all of the tests:
+
+```bash
+pushd ${ANSIBLE_COLLECTIONS_PATH};
+pytest ansible_collections/cloudera/cluster;
+popd;
+```
+
+To run a selected test, execute with a regex:
+
+```bash
+pushd ${ANSIBLE_COLLECTIONS_PATH};
+pytest ansible_collections/cloudera/cluster -k "test_assemble_cluster_template_module"
+popd;
+```