# Device Under Test
URL: /dut

Learn how to track the serial number of the Unit Under Test (UUT) with OpenHTF for better traceability during test execution.

Track the serial number of the unit under test with each run.

When running tests, tracking serial numbers is important for traceability. With OpenHTF, you can either manually enter the serial number at the start of the test or set it programmatically during the test.

You can prompt the operator to input the serial number manually at the start of the test.

When executed, the script prompts the user to enter a serial number. The prompt is a regular phase returned by `prompt_for_test_start()`, and it takes options:

Prompt text. Default: `'Enter a DUT ID in order to start the test.'`

Seconds to wait before the start phase times out. Default: 24 hours.

Function applied to the typed string; its return value becomes the DUT ID. Raise to reject the input and re-prompt. Default: identity.

A barcode scanner in keyboard-wedge mode types the serial and presses Enter, so this prompt works unchanged on the production floor.

You can set the serial number at the start of the test.

You can set the serial number during the test, for example after reading it from the device over a serial link or from an EEPROM.

If no start trigger and no phase sets `dut_id`, OpenHTF records `UNKNOWN_DUT`. Override that fallback with `test.configure(default_dut_id="...")` — see Test Options. The `ignore_early_canceled_tests` example uses it to drop records for tests aborted before an operator scanned anything.

<Card title="Plugs" href="/plugs" description="The UserInput plug behind prompt_for_test_start()." />

<Card title="Operator UI" href="/operator-ui" description="The same prompt rendered in the browser." />

<Card title="Test Record" href="/test-record" description="dut_id is the first field of every record." />