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Writing tests

The idea

A test plays both sides of a Zigbee conversation. createVirtualDevice() in test/util/virtualDevice.js creates two nodes linked in memory:

  • zclNode, the code under test, as a Homey driver gets it.
  • virtualDevice, the device it talks to, scripted by the test with BoundClusters.

Both run the library's real encoding, parsing and response matching; only the radio is replaced. The link behaves like Homey's stack where it matters for this library: frames arrive after sendFrame resolves, so response timeouts run, and zclNode cannot send more than 82 bytes. The link also logs every frame and lets a test drop, rewrite or inject frames, which is how a test makes a device misbehave in ways real hardware rarely does.

The options and return values are documented on the functions in test/util/virtualDevice.js.

Examples

To test See
A command or attribute read test/onOff.js
The bytes on the wire against the specification test/colorControl.js
A report or notification from the device test/attributeReport.js
A device that answers wrongly, or never; known bugs as todo test/virtualDevice.js
Colliding TSNs, duplicate responses, failed sends test/testClusterResponseTimeout.js
Group and broadcast frames test/testNode.js
Homey serving the device, such as OTA test/ota.js
A cluster with its own data type test/xiaomiLifeline.js

Rules

A test is only worth having if it fails when the code it covers breaks.

  • Never assert inside a handler. The endpoint turns a thrown assertion into an error Default Response, so the test may pass anyway. Store what the handler got and assert after the await.
  • No done callbacks. Await the command, or settle().
  • await settle() before asserting that something did not happen, or on what a frame from the device triggered.
  • Fake time with t.mock.timers, never wait for a real timeout.
  • One device per test, created inside the it.
  • Assert specific errors and real bytes. A round trip through the same definition passes when the definition is wrong.
  • Prove the failure path. Break the library code under test and check the test fails.
  • A known bug is a test for the correct behavior marked { todo: '...' }. Check it fails on the bug, not on the test; the fix removes the todo.