# 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

1. **Nothing open-source** — libplctag's test suite runs against real
   hardware; there is no public PCCC simulator comparable to `pymodbus` or
   `ab_server`.
2. **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.
3. **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