Dockerize Modbus + AB CIP + S7 test fixtures for reproducibility. Every driver integration simulator now has a pinned Docker image alongside the existing native launcher — Docker is the primary path, native fallbacks kept for contributors who prefer them. Matches the already-Dockerized OpcUaClient/opc-plc pattern from #215 so every fixture in the fleet presents the same compose-up/test/compose-down loop. Reproducibility gain: what used to require a local pip/Python install (Modbus pymodbus, S7 python-snap7) or a per-OS C build from source (AB CIP ab_server from libplctag) now collapses to a Dockerfile + docker compose up. Modbus — new tests/ZB.MOM.WW.OtOpcUa.Driver.Modbus.IntegrationTests/Docker/ with Dockerfile (python:3.12-slim-bookworm + pymodbus[simulator]==3.13.0) + docker-compose.yml with four compose profiles (standard / dl205 / mitsubishi / s7_1500) backed by the existing profile JSONs copied under Docker/profiles/ as canonical; native fallback in Pymodbus/ retained with the same JSON set (symlink-equivalent — manual re-sync when profiles change, noted in both READMEs). Port 5020 unchanged so MODBUS_SIM_ENDPOINT + ModbusSimulatorFixture work without code change. Dropped the --no_http CLI arg the old serve.ps1 + compose draft passed — pymodbus 3.13 doesn't recognize it; the simulator's http ui just binds inside the container where nothing maps it out and costs nothing. S7 — new tests/ZB.MOM.WW.OtOpcUa.Driver.S7.IntegrationTests/Docker/ with Dockerfile (python:3.12-slim-bookworm + python-snap7>=2.0) + docker-compose.yml with one s7_1500 compose profile; copies the existing server.py shim + s7_1500.json seed profile; runs python -u server.py ... --port 1102. Native fallback in PythonSnap7/ retained. Port 1102 unchanged. AB CIP — hardest because ab_server is a source-only C tool in libplctag's src/tools/ab_server/. New tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests/Docker/ Dockerfile is multi-stage: build stage (debian:bookworm-slim + build-essential + cmake) clones libplctag at a pinned tag + cmake --build build --target ab_server; runtime stage (debian:bookworm-slim) copies just the binary from /src/build/bin_dist/ab_server. docker-compose.yml ships four compose profiles (controllogix / compactlogix / micro800 / guardlogix) with per-family ab_server CLI args matching AbServerProfile.cs. AbServerFixture updated: tries TCP probe on 127.0.0.1:44818 first (Docker path) + spawns the native binary only as fallback when no listener is there. AB_SERVER_ENDPOINT env var supported for pointing at a real PLC. AbServerFact/Theory attributes updated to IsServerAvailable() which accepts any of: live listener on 44818, AB_SERVER_ENDPOINT set, or binary on PATH. Required two CLI-compat fixes to ab_server's argument expectations that the existing native profile never caught because it was never actually run at CI: --plc is case-sensitive (ControlLogix not controllogix), CIP tags need [size] bracket notation (DINT[1] not bare DINT), ControlLogix also requires --path=1,0. Compose files carry the corrected flags; the existing native-path AbServerProfile.cs was never invoked in practice so we don't rewrite it here. Micro800 now uses the --plc=Micro800 mode rather than falling back to ControlLogix emulation — ab_server does have the dedicated mode, the old Notes saying otherwise were wrong. Updated docs: three fixture coverage docs (Modbus-Test-Fixture.md, S7-Test-Fixture.md, AbServer-Test-Fixture.md) flip their "What the fixture is" section from native-only to Docker-primary-with-native-fallback; dev-environment.md §Resource Inventory replaces the old ambiguous "Docker Desktop + ab_server native" mix with four per-driver rows (each listing the image, compose file, compose profiles, port, credentials) + a new Docker fixtures — quick reference subsection giving the one-line docker compose -f <…> --profile <…> up for each driver + the env-var override names + the native fallback install recipes. drivers/README.md coverage map table updated — Modbus/AB CIP/S7 entries now read "Dockerized …" consistent with OpcUaClient's line. Verified end-to-end against live containers: Modbus DL205 smoke 1/1, S7 3/3, AB CIP ControlLogix 4/4 (all family theory rows). Container lifecycle clean (up/test/down, no leaked state). Every fixture keeps its skip-when-absent probe + env-var endpoint override so dotnet test on a fresh clone without Docker running still gets a green run.

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

tests/ZB.MOM.WW.OtOpcUa.Driver.Modbus.IntegrationTests/Docker/Dockerfile

@@ -0,0 +1,27 @@
+# pymodbus simulator container for the Modbus integration suite.
+#
+# Pinned base + package version so the fixture surface is reproducible —
+# matches the version referenced in tests/.../Pymodbus/README.md.
+FROM python:3.12-slim-bookworm
+
+LABEL org.opencontainers.image.source="https://github.com/dohertj2/lmxopcua" \
+      org.opencontainers.image.description="pymodbus simulator for OtOpcUa Modbus driver integration tests"
+
+RUN pip install --no-cache-dir "pymodbus[simulator]==3.13.0"
+
+# Ship every profile in the image so one container can serve whichever
+# family a test run needs; the compose file picks which JSON is active via
+# the command override.
+WORKDIR /fixtures
+COPY profiles/ /fixtures/
+
+EXPOSE 5020
+
+# Default to the standard profile; docker-compose.yml overrides per service.
+# --http_port intentionally omitted; pymodbus 3.13's web UI binds on a
+# container-local default we don't publish, so it's not reachable from the
+# host and costs nothing.
+CMD ["pymodbus.simulator", \
+     "--modbus_server", "srv", \
+     "--modbus_device",  "dev", \
+     "--json_file",      "/fixtures/standard.json"]