The fixture Agent flips to AllowPut = true (its comment rewritten: writes are in
scope now that the driver implements IWritable) and the suite grows three
env-gated write legs, all still Assert.Skip-clean with no Agent reachable.
Devices.xml gains a DataItem, and that is the deliberate part. The write target
has to be one the SHDR adapter NEVER feeds, or the assertion races the stream --
but it must NOT be the existing never-fed fixture_block: the first successful
write takes an item off UNAVAILABLE for the life of the container, which would
silently rob Read_maps_an_unavailable_observation_to_BadNoCommunication of its
subject. So fixture_writeback (free-text EVENT, PROGRAM_COMMENT) is a separate,
dedicated target, overridable via MTCONNECT_WRITE_TARGET for a run pointed at a
real machine tool.
The three legs:
* Round trip -- driver write accepted, then the injected value read back off
/current over plain HTTP (not through the parser under test) AND through the
driver's own ReadAsync. The value carries a TickCount64 suffix: the Agent
keeps an injected observation for the container's life, so a constant would
be satisfied by a previous run's leftover.
* Agent refusal -> BadCommunicationError. The design doc doubted this leg was
constructible ("an id in the probe but refused by the agent"); it is, and the
mechanism is BuildWriteTargets. Write targets are derived from the tags the
BINDING serves, with the device resolved from the probe model and falling
back to the configured deviceName -- so an authored tag naming an id the
Agent never declared, on a driver whose deviceName IS set, resolves to a real
URL and is POSTed. That is exactly the shape a stale tag has after a DataItem
is renamed. The second half of the test is the falsifiability control: the
SAME unknown id with NO deviceName has no URL and must be refused locally as
BadNodeIdUnknown. Two different codes is what proves the first write actually
reached the Agent rather than being short-circuited into a look-alike.
* Disabled gate -- write.enabled absent returns BadNotWritable AND /current is
unchanged from the snapshot taken just before, which is what distinguishes
"refused" from "reported refused and sent anyway".
RAN LIVE, not just compiled: the fixture was brought up locally (OrbStack,
MTCONNECT_AGENT_HOST_PORT=5555 -- macOS AirPlay squats :5000) and the whole
suite passed 15/15, 0 skipped. Evidence beyond the green: the Agent reports
<ProgramComment dataItemId="fixture_writeback">OTOPCUA-WRITE-2CBCB530</...> and
its log carries "Error processing request:
/OtFixtureCnc?otopcua_no_such_data_item_2CBCB3D9=refuse-me" -- the refusal leg
demonstrably went to the wire. Offline (no Agent) the suite is 15 skipped, 0
failed; build 0 warnings / 0 errors.
Note for anyone reading agent.cfg: BufferSize = 14 is an EXPONENT (2^14 = 16384
observations), not a 14-deep ring, and /current is answered from the Agent's
per-DataItem checkpoint anyway -- so eviction is not a hazard for a write
read-back even on this busy fixture stream.
LiveOptions/ConfigJson/LiveDriverAsync gained writeEnabled + deviceName
parameters, both defaulted off/null so every pre-existing test still runs
against the shipped read-only driver whatever the Agent's AllowPut says. The
config JSON sources write.enabled FROM the options object, so the parsed config
can never disagree with the options a test thinks it built.
The first and only thing in the MTConnect workstream that exercises the driver
against a real Agent; everything else runs on canned XML.
Fixture (Docker/): two services, both stock images with this folder bind-mounted.
- `agent` mtconnect/agent:2.7.0.12 on :5000. NOTE the repo name: the source
project is mtconnect/cppagent but the PUBLISHED image is
mtconnect/agent; mtconnect/cppagent does not exist on Docker Hub.
- `adapter` a stdlib SHDR feeder. Required, not optional: the agent image ships
only the binary + schemas/styles, so a lone Agent answers /probe and
then reports every observation UNAVAILABLE forever, which can prove
nothing about reads or streaming.
Devices.xml seeds one DataItem per inference branch (SAMPLE+units, TIME_SERIES,
PART_COUNT/LINE_NUMBER, controlled vocab, DATA_SET, CONDITION), gives every named
item `name != id` (the inverse of the hand-authored unit fixtures), and leaves one
EVENT permanently unfed so UNAVAILABLE -> BadNoCommunication has a live subject.
Suite (12 tests) asserts STRUCTURALLY against the Agent's own /probe response, never
by literal id, so it survives an edit to Devices.xml and can be pointed at a real
machine tool via MTCONNECT_AGENT_ENDPOINT. It skips cleanly (12/12) when no Agent
answers, and each test carries a hard [Fact(Timeout)] so a half-up fixture cannot
wedge a build.
Three findings from bringing the fixture up, each now pinned in a comment:
- agent.cfg must be pure ASCII; one non-ASCII byte in a COMMENT makes the config
parser reject the whole file with a bare "Failed / Stopped at line: N" and exit.
- `sampleCount` is an attribute of a TIME_SERIES observation, not of a DataItem
declaration. A real Agent meeting one on a declaration DROPS THE ENTIRE DATA ITEM
from the device model, so the inference only ever sees null and a live TIME_SERIES
tag is always variable-length. Asserted, not ignored.
- The Agent's own <Agent> self-model publishes update-rate SAMPLEs that tick whether
or not any adapter is attached. Excluding them is load-bearing: with them included
the "live stream delivered a changed value" test passed with the fixture's data
source deliberately stopped.
MTConnectError-under-HTTP-200 is NOT covered live and cannot be: cppagent 2.7 answers
an unknown device 404 and an out-of-range sequence 400, each with a well-formed error
body. That shape stays canned-only, and the suite says so.
Joseph Doherty