# AB Legacy test fixture

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

**TL;DR:** Docker integration-test scaffolding lives at
`tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.IntegrationTests/` (task #224),
reusing the AB CIP `ab_server` image in PCCC mode with per-family
compose profiles (`slc500` / `micrologix` / `plc5`). The smoke tests pass
for N-file (Int16), F-file (Float32), and L-file (Int32) reads across all
three families when `AB_LEGACY_CIP_PATH=1,0` (the default). The earlier
`BadCommunicationError` was traced to `ab_server` requiring a non-empty CIP
routing path before forwarding to the PCCC dispatcher — the `/1,0` workaround
resolves it (see `Docker/README.md §Known limitations`). Residual gap: bit-file
writes (`B3:0/5`) still surface `0x803D0000` against `ab_server`. Unit tests
via `FakeAbLegacyTag` carry full contract coverage for all paths.

## What the fixture is

**Integration layer** (task #224):
`tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.IntegrationTests/` with
`AbLegacyServerFixture` (TCP-probes `10.100.0.35:44818` — the shared Docker
host; override with `AB_LEGACY_ENDPOINT`) + three smoke tests (parametric read
across families, SLC500 write-then-read). Reuses the AB CIP
`otopcua-ab-server:libplctag-release` image via a relative `build:` context in
`Docker/docker-compose.yml` — one image, different `--plc` flags. See
`Docker/README.md §Known limitations` for the CIP-path gate + bit-file write
gap.

**Unit layer**: `tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests/` is
still the primary coverage. 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

1. **Close residual ab_server bit-file write gap** — N (Int16), F (Float32),
   and L (Int32) files round-trip cleanly across SLC500 / MicroLogix / PLC-5
   modes with the `/1,0` cip-path workaround in place. Remaining gap: bit-file
   writes (`B3:0/5`) surface `0x803D0000` against `ab_server --plc=SLC500`.
   Contributing a patch to `libplctag/libplctag` to close this would remove
   the last Docker-vs-hardware divergence for bit writes.
2. **Rockwell RSEmulate 500 golden-box tier** — Rockwell's real emulator
   for SLC/MicroLogix/PLC-5. Would close UDT-equivalent (integer-file
   indirection), timer/counter decomposition, and real ladder execution
   gaps. Costs: RSLinx OEM license, Windows-only, Hyper-V conflict
   matching TwinCAT XAR + Logix Emulate, no clean PR-diffable project
   format (SLC/ML save as binary `.RSS`). Scaffold like the Logix
   Emulate tier when operationally worth it.
3. **Lab rig** — used SLC 5/05 or MicroLogix 1100 on a dedicated
   network; parts are end-of-life but still available. PLC-5 +
   LogixPccc-mode behaviour + DF1 serial need specific controllers.

## Key fixture / config files

- `tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.IntegrationTests/AbLegacyServerFixture.cs`
  — TCP probe + skip attributes + env-var parsing
- `tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.IntegrationTests/AbLegacyReadSmokeTests.cs`
  — wire-level smoke tests; pass against the ab_server Docker fixture
  with `AB_LEGACY_COMPOSE_PROFILE` set to the running container
- `tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.IntegrationTests/Docker/docker-compose.yml`
  — compose profiles reusing AB CIP Dockerfile
- `tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.IntegrationTests/Docker/README.md`
  — known-limitations write-up + resolution paths
- `tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests/FakeAbLegacyTag.cs` —
  in-process fake + factory
- `src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy/AbLegacyDriver.cs` — scope remarks
  at the top of the file
