fix(docs): add missing testing docs

docs/development/README.md

@@ -56,7 +56,7 @@ uv pip install -e '.[base,dev,manipulation,misc,unitree,drone]'
 # setup pre-commit
 pre-commit install
 
-# test the install (takes about 3 minutes)
+# test the install (takes about 1 minute)
 uv run pytest dimos
 ```
 

docs/development/testing.md

@@ -0,0 +1,122 @@
+# Testing
+
+For development, you should install all dependencies so that tests have access to them.
+
+```bash
+uv sync --all-extras --no-extra dds
+```
+
+## Types of tests
+
+There are different types of tests based on what their goal is:
+
+| Type | Description | Mocking | Speed |
+|------|-------------|---------|-------|
+| Unit | Test a small individual piece of code | All dependencies | Very fast |
+| Integration | Test the integration between multiple units of code | Most dependencies | Some fast, some slow |
+| Functional | Test a particular desired functionality | Some dependencies | Some fast, some slow |
+| End-to-end | Test the entire system as a whole from the perspective of the user | None | Very slow |
+
+The distinction between unit, integration, and functional tests is often debated and rarely productive.
+
+Rather than waste time on classifying tests, it's better to separate tests by how they are used:
+
+* **fast tests**: tests which you can run after each code change (people often run them with filesystem watchers: whenever a file is saved, automatically run the tests)
+* **slow tests**: tests which you run every once in a while to make sure you haven't broken anything (maybe every commit, but definitely before publishing a PR)
+
+The purpose of running tests in a loop is to get immediate feedback. The faster the loop, the easier it is to identify a problem since the source is the tiny bit of code you changed.
+
+## Usage
+
+### Fast tests
+
+Run the fast tests:
+
+```bash
+./bin/pytest-fast
+```
+
+This is the same as:
+
+```bash
+pytest dimos
+```
+
+The default `addopts` in `pyproject.toml` includes a `-m` filter that excludes slow markers (like `integration`, `heavy`, `e2e`, etc.), so plain `pytest dimos` only runs fast tests.
+
+### Slow tests
+
+Run the slow tests:
+
+```bash
+./bin/pytest-slow
+```
+
+This overrides the default `-m` filter to include most markers. When writing or debugging a specific slow test, override `-m` yourself:
+
+```bash
+pytest -m integration dimos/path/to/test_something.py
+```
+
+Note: passing `-m` on the command line overrides the default from `addopts`, so you get exactly the marker set you asked for.
+
+## Writing tests
+
+Test files live next to the code they test. If you have `dimos/core/pubsub.py`, its tests go in `dimos/core/test_pubsub.py`.
+
+When writing tests you probably want to limit the run to whatever tests you're writing:
+
+```bash
+pytest -sv dimos/core/test_my_code.py
+```
+
+### Fixtures
+
+Pytest fixtures are very useful for making sure test failures don't affect other tests.
+
+Whenever you have something that needs to be cleaned up when the test is over (disconnect, close, delete temp files, etc.), you should use a fixture.
+
+Simple example code:
+
+```python
+@pytest.fixture
+def arm():
+    arm = RobotArm(device="/dev/ttyUSB0")
+    arm.connect()
+    yield arm
+    arm.disconnect()
+
+def test_arm_moves_to_position(arm):
+    arm.move_to(x=0.5, y=0.3, z=0.1)
+    assert arm.position == (0.5, 0.3, 0.1)
+```
+
+The `yield` is key: everything before it is setup, everything after is teardown. The teardown runs even if the test fails, so you never leak resources between tests.
+
+### Mocking
+
+It's easier to use the `mocker` fixture instead of `unittest.mock`. It automatically undoes all patches when the test ends, so you don't need `with` blocks.
+
+Patching a method:
+
+```python
+def test_uses_cached_position(mocker):
+    mocker.patch("dimos.hardware.RobotArm.get_position", return_value=(0.0, 0.0, 0.0))
+    arm = RobotArm()
+    assert arm.get_position() == (0.0, 0.0, 0.0)
+```
+
+There are other useful things in `mocker`, like `mocker.MagicMock()` for creating fake objects.
+
+## Useful pytest options
+
+| Option | Description |
+|--------|-------------|
+| `-s` | Show stdout/stderr output |
+| `-v` | More verbose test names |
+| `-x` | Stop on first failure |
+| `-k foo` | Only run tests matching `foo` |
+| `--lf` | Rerun only the tests that failed last time |
+| `--pdb` | Drop into the debugger when a test fails |
+| `--tb=short` | Shorter tracebacks |
+| `--durations=0` | Measure the speed of each test |