# Testing an Experiment

An experiment cannot be tried out properly without its instruments, but most of what
makes it safe to run can be checked without them: that its plan is the same every
time, that every step names a method, and that the plan survives being saved.
`ExperimentPipeline`, in `plesty.lib.test.experiment_pipeline`, runs these checks. It
never calls `run()`, so no device is needed. The words used here are introduced in
[Experiment Framework](../experiment/index.md).

| Test | Checks |
|---|---|
| `test_experiment_subclass` | the module has a public `Experiment` subclass that can be created without devices |
| `test_plan_deterministic` | `build_plan()` called twice gives the same fingerprint (`content_hash()`) |
| `test_plan_ops_resolve` | every step's `op` names a method, checked the same way `run()` checks it |
| `test_plan_serializable` | saving and loading the plan (`Plan.save`, `Plan.load`) keeps its fingerprint |
| `test_lifecycle_hooks` | `setup()` and `teardown()`, if overridden, are `async` |

An experiment module exposes one pytest test per check:

```python
# tests/test_pipeline.py
from plesty.lib.test.experiment_pipeline import ExperimentPipeline

from plesty.power_scan import PowerScan

PIPELINE = ExperimentPipeline(PowerScan, {"wavelengths": [500.0, 600.0]})


def test_experiment_subclass():
    PIPELINE.test_experiment_subclass()


def test_plan_deterministic():
    PIPELINE.test_plan_deterministic()


def test_plan_ops_resolve():
    PIPELINE.test_plan_ops_resolve()


def test_plan_serializable():
    PIPELINE.test_plan_serializable()


def test_lifecycle_hooks():
    PIPELINE.test_lifecycle_hooks()
```

The arguments after the class are passed to its constructor, here the `config` that
`PowerScan` takes. `PIPELINE.run_mock_pipeline()` runs all five checks at once.

plesty-sdk, PLESTY's developer tool, looks for these five tests and runs them as gate
`e1` of `plesty check` before the module may be published (see
[Which tests each module runs](index.md#which-tests-each-module-runs)).