en getting started more cases

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3. Test multiple data sets and boundaries

A passing “add 3 and hold for two cycles” test covers one scenario. Now check accumulation and boundaries.

Write the cases first

Input sequence	Expected final total	Scenario
0	0	Zero is valid input, not absence of input
3, 5	8	State accumulates across requests
255	255	Maximum input
255, 1	0	Overflow exactly to zero
250, 10	4	Keep the low eight bits after overflow

Derive expectations from the specification, not dut.total.U(), which would compare the DUT with itself.

Run each row with pytest

Continue in examples/getting_started/test_accumulator.py:

@pytest.mark.asyncio
@pytest.mark.parametrize("operands, expected", [
    ([0], 0),
    ([3, 5], 8),
    ([255], 255),
    ([255, 1], 0),
    ([250, 10], 4),
])
async def test_accumulator_cases(operands, expected):
    dut = TutorialDut()
    try:
        async with Execution(dut.backend):
            for operand in operands:
                dut.operand.Set(operand)
                dut.enable.Set(1)
                await ClockCycles(dut.clock, 1)
                dut.enable.Set(0)
            assert dut.total.U() == expected
    finally:
        dut.close()

python3 -m pytest -v examples/getting_started/test_accumulator.py::test_accumulator_cases

Expect five PASSED entries and 5 passed. -v lists each case. [3, 5] is a list; for operand in operands: visits its values in order. Each iteration writes input, waits for an edge, and clears enable. @pytest.mark.parametrize("operands, expected", [...]) calls the test once per row. Each invocation creates a fresh DUT, so cases do not inherit prior state.

Add a boundary case

Add ([128, 128], 0) and expect 6 passed. Writing 256 as the expectation makes only this new case fail, because an 8-bit register cannot hold 256. These tests check final state, not yet every response or whether all responses arrive. The repeated write/enable/wait/disable sequence is the next abstraction to extract: define a Driver.