Test a hysteresis band

Keep the rule independent of the sensor

The same function runs in CPython for tests and in MicroPython on the board. It takes a reading and the previous state; it does not import a pin driver or read a clock.

"""Shared CPython/MicroPython decision logic; temperatures are Celsius."""
def state_for(temperature, humidity, previous="unknown"):
    for value in (temperature, humidity):
        if isinstance(value, bool) or not isinstance(value, (int, float)) or value != value:
            return "unknown"
    if not (0 <= temperature <= 50 and 0 <= humidity <= 100):
        return "unknown"
    if temperature >= 28:
        return "warm"
    if temperature <= 26:
        return "ok"
    return previous if previous in ("ok", "warm") else "ok"

A boolean is an integer subtype in Python, but it is not a temperature reading in this interface. The explicit boolean rejection matters when a record is accidentally shaped incorrectly. NaN is rejected before comparisons; infinities fail the range check.

Replay the important transition

from policy import state_for
state = "unknown"
for temperature in [25, 27, 28, 27, 26]:
    state = state_for(temperature, 50, state)
    print(temperature, state)

Expect ok, ok, warm, warm, ok. Test the exact edges, not only a comfortable midpoint. After None, status should become unknown; the next 27 °C reading starts from that explicit state.

Try it

Change the warm threshold and return threshold together, keeping a gap between them. Add tests for the new exact boundaries before deploying. Avoid editing a separate copy of the policy in the firmware; copy the tested file to the board instead.