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Joseph Doherty 1d3544f18e S7 integration fixture — python-snap7 server closes the wire-level coverage gap (#216 ) + per-driver fixture coverage docs for every driver in the fleet. Closes #216 . Two shipments in one PR because the docs landed as I surveyed each driver's fixture + the S7 work is the first wire-level-gap closer pulled from that survey.

S7 integration — AbCip/Modbus already have real-simulator integration suites; S7 had zero wire-level coverage despite being a Tier-A driver (all unit tests mocked IS7Client). Picked python-snap7's `snap7.server.Server` over raw Snap7 C library because `pip install` beats per-OS binary-pin maintenance, the package ships a Python __main__ shim that mirrors our existing pymodbus serve.ps1 + *.json pattern structurally, and the python-snap7 project is actively maintained. New project `tests/ZB.MOM.WW.OtOpcUa.Driver.S7.IntegrationTests/` with four moving parts: (a) `Snap7ServerFixture` — collection-scoped TCP probe on `localhost:1102` that sets `SkipReason` when the simulator's not running, matching the `ModbusSimulatorFixture` shape one directory over (same S7_SIM_ENDPOINT env var override convention for pointing at a real S7 CPU on port 102); (b) `PythonSnap7/` — `serve.ps1` wrapper + `server.py` shim + `s7_1500.json` seed profile + `README.md` documenting install / run / known limitations; (c) `S7_1500/S7_1500Profile.cs` — driver-side `S7DriverOptions` whose tag addresses map 1:1 to the JSON profile's seed offsets (DB1.DBW0 u16, DB1.DBW10 i16, DB1.DBD20 i32, DB1.DBD30 f32, DB1.DBX50.3 bool, DB1.DBW100 scratch); (d) `S7_1500SmokeTests` — three tests proving typed reads + write-then-read round-trip work through real S7netplus + real ISO-on-TCP + real snap7 server. Picked port 1102 default instead of S7-standard 102 because 102 is privileged on Linux + triggers Windows Firewall prompt; S7netplus 0.20 has a 5-arg `Plc(CpuType, host, port, rack, slot)` ctor that lets the driver honour `S7DriverOptions.Port`, but the existing driver code called the 4-arg overload + silently hardcoded 102. One-line driver fix (S7Driver.cs:87) threads `_options.Port` through — the S7 unit suite (58/58) still passes unchanged because every unit test uses a fake IS7Client that never sees the real ctor. Server seed-type matrix in `server.py` covers u8 / i8 / u16 / i16 / u32 / i32 / f32 / bool-with-bit / ascii (S7 STRING with max_len header). register_area takes the SrvArea enum value, not the string name — a 15-minute debug after the first test run caught that; documented inline.

Per-driver test-fixture coverage docs — eight new files in `docs/drivers/` laying out what each driver's harness actually benchmarks vs. what's trusted from field deployments. Pattern mirrors the AbServer-Test-Fixture.md doc that shipped earlier in this arc: TL;DR → What the fixture is → What it actually covers → What it does NOT cover → When-to-trust table → Follow-up candidates → Key files. Ugly truth the survey made visible: Galaxy + Modbus + (now) S7 + AB CIP have real wire-level coverage; AB Legacy / TwinCAT / FOCAS / OpcUaClient are still contract-only because their libraries ship no fake + no open-source simulator exists (AB Legacy PCCC), no public simulator exists (FOCAS), the vendor SDK has no in-process fake (TwinCAT/ADS.NET), or the test wiring just hasn't happened yet (OpcUaClient could trivially loopback against this repo's own server — flagged as #215). Each doc names the specific follow-up route: Snap7 server for S7 (done), TwinCAT 3 developer-runtime auto-restart for TwinCAT, Tier-C out-of-process Host for FOCAS, lab rigs for AB Legacy + hardware-gated bits of the others. `docs/drivers/README.md` gains a coverage-map section linking all eight. Tracking tasks #215-#222 filed for each PR-able follow-up.

Build clean (driver + integration project + docs); S7.Tests 58/58 (unchanged); S7.IntegrationTests 3/3 (new, verified end-to-end against a live python-snap7 server: `driver_reads_seeded_u16_through_real_S7comm`, `driver_reads_seeded_typed_batch`, `driver_write_then_read_round_trip_on_scratch_word`). Next fixture follow-up is #215 (OpcUaClient loopback against own server) — highest ROI of the remaining set, zero external deps.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

2026-04-20 11:29:15 -04:00

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AB Legacy test fixture

Coverage map + gap inventory for the AB Legacy (PCCC) driver — SLC 500 / MicroLogix / PLC-5 / LogixPccc-mode.

TL;DR: there is no integration fixture. Everything runs through a FakeAbLegacyTag injected via IAbLegacyTagFactory. libplctag powers the real wire path but ships no in-process fake, and ab_server has no PCCC emulation either — so PCCC behavior against real hardware is trusted from field deployments, not from CI.

What the fixture is

Nothing at the integration layer. tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests/ is unit-only, all tests tagged [Trait("Category", "Unit")]. The driver accepts IAbLegacyTagFactory via ctor DI; every test supplies a FakeAbLegacyTag.

What it actually covers (unit only)

AbLegacyAddressTests — PCCC address parsing for SLC / MicroLogix / PLC-5 / LogixPccc-mode (N7:0, F8:12, B3:0/5, etc.)
AbLegacyCapabilityTests — data type mapping, read-only enforcement
AbLegacyReadWriteTests — read + write happy + error paths against the fake
AbLegacyBitRmwTests — bit-within-DINT read-modify-write serialization via per-parent SemaphoreSlim (mirrors the AB CIP + FOCAS PMC-bit pattern from #181)
AbLegacyHostAndStatusTests — probe + host-status transitions driven by fake-returned statuses
AbLegacyDriverTests — IDriver lifecycle

Capability surfaces whose contract is verified: IDriver, IReadable, IWritable, ITagDiscovery, ISubscribable, IHostConnectivityProbe, IPerCallHostResolver.

What it does NOT cover

1. Wire-level PCCC

No PCCC frame is sent by the test suite. libplctag's PCCC subset (DF1, ControlNet-over-EtherNet, PLC-5 native EtherNet) is untested here; driver-side correctness depends on libplctag being correct.

2. Family-specific behavior

SLC 500 timeout + retry thresholds (SLC's comm module has known slow-response edges) — unit fakes don't simulate timing.
MicroLogix 1100 / 1400 max-connection-count limits — not stressed.
PLC-5 native EtherNet connection setup (PCCC-encapsulated-in-CIP vs raw CSPv4) — routing covered at parse level only.

3. Multi-device routing

IPerCallHostResolver contract is verified; real PCCC wire routing across multiple gateways is not.

4. Alarms / history

PCCC has no alarm object + no history object. Driver doesn't implement IAlarmSource or IHistoryProvider — no test coverage is the correct shape.

5. File-type coverage

PCCC has many file types (N, F, B, T, C, R, S, ST, A) — the parser tests cover the common ones but uncommon ones (R counters, S status files, A ASCII strings) have thin coverage.

When to trust AB Legacy tests, when to reach for a rig

Question	Unit tests	Real PLC
"Does `N7:0/5` parse correctly?"	yes	-
"Does bit-in-word RMW serialize concurrent writers?"	yes	yes
"Does the driver lifecycle hang / crash?"	yes	yes
"Does a real read against an SLC 500 return correct bytes?"	no	yes (required)
"Does MicroLogix 1100 respect its connection-count cap?"	no	yes (required)
"Do PLC-5 ST-files round-trip correctly?"	no	yes (required)

Follow-up candidates

Nothing open-source — libplctag's test suite runs against real hardware; there is no public PCCC simulator comparable to pymodbus or ab_server.
Lab rig — cheapest path is a used SLC 5/05 or MicroLogix 1100 on a dedicated network; the parts are end-of-life but still available. PLC-5 and LogixPccc-mode behavior require those specific controllers.
libplctag upstream test harness — the project's own tests/ folder has PCCC cases we could try to adapt, but they assume specific hardware.

AB Legacy is inherently a trust-the-library driver until someone stands up a rig.

Key fixture / config files

tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests/FakeAbLegacyTag.cs — in-process fake + factory
src/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy/AbLegacyDriver.cs — scope remarks at the top of the file

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