# 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/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`). Scaffold passes
the skip-when-absent contract cleanly. **Wire-level round-trip against
`ab_server` PCCC mode currently fails** with `BadCommunicationError`
on read/write (verified 2026-04-20) — ab_server's PCCC server-side
coverage is narrower than libplctag's PCCC client expects. The smoke
tests target the correct shape for real hardware + should pass when
`AB_LEGACY_ENDPOINT` points at a real SLC 5/05 / MicroLogix. Unit tests
via `FakeAbLegacyTag` still carry the contract coverage.

## What the fixture is

**Integration layer** (task #224, scaffolded with a known ab_server
gap):
`tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.IntegrationTests/` with
`AbLegacyServerFixture` (TCP-probes `localhost:44818`) + 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
ab_server PCCC round-trip gap + resolution paths.

**Unit layer**: `tests/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. **Fix ab_server PCCC coverage upstream** — the scaffold lands the
   Docker infrastructure; the wire-level round-trip gap is in ab_server
   itself. Filing a patch to `libplctag/libplctag` to expand PCCC
   server-side opcode coverage would make the scaffolded smoke tests
   pass without a golden-box tier.
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/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.IntegrationTests/AbLegacyServerFixture.cs`
  — TCP probe + skip attributes + env-var parsing
- `tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.IntegrationTests/AbLegacyReadSmokeTests.cs`
  — three wire-level smoke tests (currently blocked by ab_server PCCC gap)
- `tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.IntegrationTests/Docker/docker-compose.yml`
  — compose profiles reusing AB CIP Dockerfile
- `tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.IntegrationTests/Docker/README.md`
  — known-limitations write-up + resolution paths
- `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
