What a production test plan is
A production test plan is a written document that defines what every shipped unit has to pass before it gets a serial number and a label.
It includes:
- Test setup (instruments, fixture, environment)
- Test sequence (which test runs first, second, third)
- Pass and fail criteria per test (numeric ranges, expected values, tolerances)
- Defect routing (what happens when a test fails)
- Calibration steps (per-unit calibration if any)
- Logging (what gets written to the traceability database)
It is typically 5 to 20 pages depending on product complexity.
What happens without one
Without a production test plan, the only quality gates are AOI (placement and joint inspection) and visual final inspection. Both miss firmware behavior, sensor accuracy, RF performance, and analog signal integrity.
Units leave the line that look fine but do not work. Defects show up at the integrator (next stage in the supply chain) or at the end customer. Cost escalates 10x at each step.
What goes in the test plan
A connected device test plan typically covers:
Power-on and boot
- Bootloader runs to expected version and hash
- Application boots to known service state
- Boot-time error count is zero
Sensors and inputs
- Each sensor reads a reference value within tolerance
- Each input pin reads a known state correctly
- Calibration coefficients computed and stored if applicable
Outputs
- Each output drives to expected level
- Relays switch and verify continuity
- Display shows expected pattern
RF (if applicable)
- TX power within tolerance against golden unit
- RX sensitivity within tolerance
- Modulation correct on spectrum analyzer
Power consumption
- Idle current within spec
- Active current within spec
- Sleep mode entry and exit work
Communication
- UART, SPI, I2C, USB enumeration as expected
- Network registration if applicable
When to write the test plan
As early as you can in NPI. The test plan drives:
- Test fixture design (which signals need to be probed)
- Firmware design (which test modes need to exist)
- Production cycle time estimates
- Cost estimates for the line
A test plan written at production launch is too late. Things have already been designed without test in mind.
What good test plans share
- Specific numeric criteria, not "looks good"
- Reference to a golden unit or calibrated reference
- Defined response to each failure mode
- Per-unit logging defined upfront
- Reviewed by both engineering and production
- Updated as the product evolves