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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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TwinCAT test fixture

Coverage map + gap inventory for the Beckhoff TwinCAT ADS driver.

TL;DR: there is no integration fixture. Every test uses a FakeTwinCATClient injected via ITwinCATClientFactory. Beckhoff's ADS library has no open-source simulator; ADS traffic against real TwinCAT runtimes is trusted from field deployments.

The silver lining: TwinCAT is the only driver outside Galaxy that uses native notifications (no polling) for ISubscribable, and the fake exposes a fire-event harness so notification routing is contract-tested rigorously — just not on the wire.

What the fixture is

Nothing at the integration layer. tests/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests/ is unit-only. FakeTwinCATClient also fakes the AddDeviceNotification flow so tests can trigger callbacks without a running runtime.

What it actually covers (unit only)

TwinCATAmsAddressTests — ads://<netId>:<port> parsing + routing
TwinCATCapabilityTests — data-type mapping (primitives + declared UDTs), read-only classification
TwinCATReadWriteTests — read + write through the fake, status mapping
TwinCATSymbolPathTests — symbol-path routing for nested struct members
TwinCATSymbolBrowserTests — ITagDiscovery.DiscoverAsync via ReadSymbolsAsync (#188) + system-symbol filtering
TwinCATNativeNotificationTests — AddDeviceNotification (#189) registration, callback-delivery-to-OnDataChange wiring, unregister on unsubscribe
TwinCATDriverTests — IDriver lifecycle

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

What it does NOT cover

1. AMS / ADS wire traffic

No real AMS router frame is exchanged. Beckhoff's TwinCAT.Ads NuGet (their own .NET SDK, not libplctag-style OSS) has no in-process fake; tests stub the ITwinCATClient abstraction above it.

2. Multi-route AMS

ADS supports chained routes (<localNetId> → <routerNetId> → <targetNetId>) for PLCs behind an EC master / IPC gateway. Parse coverage exists; wire-path coverage doesn't.

3. Notification reliability under jitter

AddDeviceNotification delivers at the runtime's cycle boundary; under high CPU load or network jitter real notifications can coalesce. The fake fires one callback per test invocation — real callback-coalescing behavior is untested.

4. TC2 vs TC3 variant handling

TwinCAT 2 (ADS v1) and TwinCAT 3 (ADS v2) have subtly different GetSymbolInfoByName semantics + symbol-table layouts. Driver targets TC3; TC2 compatibility is not exercised.

5. Cycle-time alignment for `ISubscribable`

Native ADS notifications fire on the PLC cycle boundary. The fake test harness assumes notifications fire on a timer the test controls; cycle-aligned firing under real PLC control is not verified.

6. Alarms / history

Driver doesn't implement IAlarmSource or IHistoryProvider — not in scope for this driver family. TwinCAT 3's TcEventLogger could theoretically back an IAlarmSource, but shipping that is a separate feature.

When to trust TwinCAT tests, when to reach for a rig

Question	Unit tests	Real TwinCAT runtime
"Does the AMS address parser accept X?"	yes	-
"Does notification → `OnDataChange` wire correctly?"	yes (contract)	yes
"Does symbol browsing filter TwinCAT internals?"	yes	yes
"Does a real ADS read return correct bytes?"	no	yes (required)
"Do notifications coalesce under load?"	no	yes (required)
"Does a TC2 PLC work the same as TC3?"	no	yes (required)

Follow-up candidates

TwinCAT 3 runtime on CI — Beckhoff ships a free developer runtime (7-day trial, restartable). Could run on a Windows CI runner with a helper that auto-restarts the runtime every 6 days. Works but operational overhead.
AdsSimulator — Beckhoff has a closed-source "ADS simulator" library used internally; not publicly available.
Lab rig — cheapest IPC (CX7000 / CX9020) on a dedicated network; the only route that covers TC2 + real notification behavior + EtherCAT I/O effects.

Without a rig, TwinCAT correctness is trusted from the fake matching reality, which has held across field deployments so far.

Key fixture / config files

tests/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests/FakeTwinCATClient.cs — in-process fake with the notification-fire harness used by TwinCATNativeNotificationTests
src/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT/TwinCATDriver.cs — ctor takes ITwinCATClientFactory

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