Joseph Doherty
e77bca385a
- Galaxy: deadline bounds the wait, not the subscribe RPC; BadTimeout for all tags and late handles unsubscribed; doc comment relocated - S7: probe connect runs on the connect deadline so a timeout opens the backoff window - S7: a successful write only retires a Faulted the write side owns - S7: null array elements rejected (BadTypeMismatch); multi-PDU array writes documented non-atomic - S7 integration: array write test gated on S7_SIM_ALLOW_WRITES=1 Claude-Session: https://claude.ai/code/session_01Ef2ozxS7QPanGT8uoATbTe
6.6 KiB
Siemens S7 test fixture
Coverage map + gap inventory for the S7 driver.
TL;DR: S7 now has a wire-level integration fixture backed by
python-snap7's Server class
(task #216). Atomic reads (u16 / i16 / i32 / f32 / bool-with-bit) + DB
write-then-read round-trip are exercised end-to-end through S7netplus +
real ISO-on-TCP on 10.100.0.35:1102 (the shared Docker host; override via
S7_SIM_ENDPOINT). Unit tests still carry everything else (address parsing,
error-branch handling, probe-loop contract). Gaps remaining are
variant-quirk-shaped: Optimized-DB symbolic access, PG/OP session types,
PUT/GET-disabled enforcement — all need real hardware.
What the fixture is
Integration layer (task #216):
tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.S7.IntegrationTests/ stands up a
python-snap7 Server via Docker/docker-compose.yml --profile s7_1500
on 10.100.0.35:1102 (the shared Docker host; override via S7_SIM_ENDPOINT;
pinned python:3.12-slim-bookworm base +
python-snap7>=2.0). Docker is the only supported launch path.
Tests that WRITE to the endpoint (currently S7_1500ArrayWriteTests) additionally require
S7_SIM_ALLOW_WRITES=1, because S7_SIM_ENDPOINT can be pointed at a real CPU; they skip without it.
Snap7ServerFixture probes the port at collection init + skips with a
clear message when unreachable (matches the pymodbus pattern).
server.py (baked into the image under Docker/) reads a JSON profile
- seeds DB/MB bytes at declared offsets; seeds are typed (
u16/i16/i32/f32/bool/asciifor S7 STRING).
Unit layer: tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.S7.Tests/ covers
everything the wire-level suite doesn't — address parsing, error
branches, probe-loop contract. All tests tagged
[Trait("Category", "Unit")].
The driver ctor change that made this possible:
Plc(CpuType, host, port, rack, slot) — S7netplus 0.20's 5-arg overload
— wires S7DriverOptions.Port through so the simulator can bind 1102
(non-privileged) instead of 102 (root / Firewall-prompt territory).
What it actually covers
Integration (python-snap7, task #216)
S7_1500SmokeTests.Driver_reads_seeded_u16_through_real_S7comm— DB1.DBW0 read via real S7netplus over TCP + simulator; proves handshake + read pathS7_1500SmokeTests.Driver_reads_seeded_typed_batch— i16, i32, f32, bool-with-bit in one batch call; proves typed decode per S7DataTypeS7_1500SmokeTests.Driver_write_then_read_round_trip_on_scratch_word—DB1.DBW100write → read-back; proves write path + buffer visibility
Unit
S7AddressParserTests— S7 address syntax (DB1.DBD0,M10.3,IW4, etc.)S7DriverScaffoldTests—IDriverlifecycle (init / reinit / shutdown / health)S7DriverReadWriteTests— error paths (uninitialized read/write, bad addresses, transport exceptions)S7DiscoveryAndSubscribeTests—ITagDiscovery.DiscoverAsync+ polledISubscribablecontract with the sharedPollGroupEngine
Capability surfaces whose contract is verified: IDriver, ITagDiscovery,
IReadable, IWritable, ISubscribable, IHostConnectivityProbe.
Wire-level surfaces verified: IReadable, IWritable.
What it does NOT cover
1. Wire-level anything (unit tests only)
The unit suite (S7DriverReadWriteTests, etc.) sends no real ISO-on-TCP
frames. S7netplus has no in-process fake mode; units contract-test via the
IS7Client abstraction. The integration suite (S7_1500SmokeTests, task
#216) does send real S7comm over ISO-on-TCP against the python-snap7 container
and covers the basic read / write / typed-batch path.
2. Error-branch unit tests vs. real round-trips
S7DriverReadWriteTests (unit) exercises error paths only; return values come
from the fake. The integration suite exercises the successful read / write
round-trip, but only against the python-snap7 emulator — not a real Siemens
CPU.
3. Mailbox serialization under concurrent reads
The driver's SemaphoreSlim serializes S7netplus calls because the S7 CPU's
comm mailbox is scanned at most once per cycle. Contention behavior under
real PLC latency is not exercised.
4. Variant quirks
S7-1200 vs S7-1500 vs S7-300/400 connection semantics (PG vs OP vs S7-Basic) not differentiated at test time.
5. Data types beyond the scalars
UDT fan-out, STRING with length-prefix quirks, DTL / DATE_AND_TIME,
arrays of structs — not covered.
When to trust the S7 tests, when to reach for a rig
| Question | Unit tests | Integration (python-snap7) | Real PLC |
|---|---|---|---|
| "Does the address parser accept X syntax?" | yes | - | - |
| "Does the driver lifecycle hang / crash?" | yes | yes | yes |
| "Does a real read against an S7-1500 return correct bytes?" | no | yes (basic scalars) | yes (required for full type matrix) |
| "Does mailbox serialization actually prevent PG timeouts?" | no | no | yes (required) |
| "Does a UDT fan-out produce usable member variables?" | no | no | yes (required) |
Follow-up candidates
The python-snap7 fixture (task #216) covers scalar read / write / typed-batch. Remaining gaps need one of:
- Plcsim Advanced — Siemens' paid emulator; gives Optimized-DB symbolic access + PG/OP/S7-Basic session differentiation without real hardware. Licensed per-seat; fits a lab rig but not CI.
- Real S7 lab rig — cheapest physical PLC (CPU 1212C) on a dedicated network port, wired via self-hosted runner. Only path for mailbox serialization / PUT-GET enforcement verification.
Without either, S7 driver correctness for variant-quirk edge cases is trusted from field deployments, not from the test suite.
Key fixture / config files
tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.S7.Tests/— unit tests only, no harnesstests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.S7.IntegrationTests/Snap7ServerFixture.cs— collection fixture; parsesS7_SIM_ENDPOINT(default10.100.0.35:1102), TCP-probes at collection init, recordsSkipReasonwhen unreachabletests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.S7.IntegrationTests/S7_1500/S7_1500SmokeTests.cs— wire-level test suite (3[Fact]methods: u16 read, typed batch, write-then-read)tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.S7.IntegrationTests/Docker/docker-compose.yml— one service per profile (s7_1500); binds1102:1102on the Docker hosttests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.S7.IntegrationTests/Docker/profiles/s7_1500.json— DB1 + MB seed layout with typed seeds at known offsetssrc/Drivers/ZB.MOM.WW.OtOpcUa.Driver.S7/S7Driver.cs— ctor takesIS7ClientFactorywhich tests fake