Stress testing

Stress suite. Hammers app parts των οποίων η αποτυχία κοστίζει στους χρήστες χρήματα — chiefly copy trading — με hostile, randomized, fault-injected workloads. Asserts system stay correct. Lives in tests/StressTests, τρέχει στο normal dotnet test green gate.

Approach — Deterministic Simulation Testing (DST)

Best way να stress distributed financial systems = deterministic simulation testing, per TigerBeetle, FoundationDB, Antithesis: run real logic against simulated world, drive με seeded random workload + injected faults, assert invariants at quiescence. All seeded + deterministic → any failure reproduces exact from seed. Combined with:

• Chaos-engineering fault injection (Netflix Chaos Monkey style) — connection drops, order rejections, token rotation, node death.
• Property-based invariants — no assert exact call sequences· assert properties that must hold no matter how events interleave (convergence, no orphans, at-most-one lease holder).

Η app ήδη ships perfect DST world model: FakeTradingSession, cTrader-faithful in-memory Open API session. Stress suite επαναχρησιμοποιεί αυτό (linked, single source of truth) not mock, οπότε simulated broker behaves like real one.

What it covers

Copy trading (primary focus)

Driven via CopyDstWorld (tests/StressTests/CopyTrading/), runs live CopyEngineHost against fake session, issues membership-consistent source workload:

Scenario	Stresses
Mass_fan_out…	1 source → 80 destinations, 150 opens then closes· full fan-out + drain
High_frequency_open_close…	300 rapid interleaved open/close· no leaked positions
Partial_close_and_scale_in_storm…	partial-close + scale-in churn· label-set stability
Connection_flap_storm…	repeated socket disconnect/reconnect + mid-flight desync· resync convergence
Order_rejection_cascade…	a subset rejects every order· healthy destinations unaffected, then self-heal via resync
Token_rotation_storm…	rapid in-place token swaps during an order storm
Randomized_chaos_workload… (10 seeds)	the DST core — every event type + every fault interleaved unpredictably
CopyLeaseReclaimStressTests	node death + lease reclaim across a scaled cluster (pure domain, FakeTimeProvider)

Convergence invariant. At rest, every healthy destination mirrors exactly set of still-open source positions — no orphans, none missing. Asserted on label set (scale-in legitimately opens second destination position under same source label, so duplicate labels expected). Destination currently rejecting orders allowed to lag, reconciled once healed.

Lease invariant. In cluster where nodes die + revive on seeded schedule, at most one node ever holds valid lease on a profile· dead node's lease lapses exact at expiry, gets reclaimed· healthy cluster settles with every profile held by exact one node. Mirrors CopyEngineSupervisor's claim predicate against CopyProfile domain lease methods.

Thread-safety of the harness

FakeTradingSession single-threaded· stress workload mutates it from test thread while host reads/writes from its loop. SyncTradingSession wraps it, makes every session operation atomic on one gate (without holding gate across reconnect callback — would invert lock order vs host's _stateGate and deadlock). Simulator itself left untouched.

Bugs found

• Startup resync race in CopyEngineHost. OnReconnected wired before initial reference-load + first resync, which ran without _stateGate. Socket flap during startup ran second resync concurrent, corrupted host's non-concurrent state dicts (_symbolDetails, _sourceVolumes). Fixed: run startup load + first resync under gate. Production race, not test artifact — DST chaos workload surfaced it.

Running

dotnet test tests/StressTests/StressTests.csproj

Suite serialized ([assembly: CollectionBehavior(DisableTestParallelization = true)]): each test spins live host background loop, drives to quiescence under wall clock, so parallel run starves host tasks and makes convergence timeouts flaky. Workloads sized to finish in seconds so suite stays in default green gate. Failure prints its seed· re-run that seed to reproduce exact interleaving.

Extending

• New copy behavior → add source op to CopyDstWorld (keep source book membership consistent with event stream) + weighted case in CopyChaosDstTests. If it can create or retire a destination position, make sure convergence invariant still holds.
• New fault → add injector to CopyDstWorld (delegate to FakeTradingSession's control surface via SyncTradingSession) + exercise in a named scenario plus chaos mix.
• Keep simulator cTrader-faithful (δείτε root CLAUDE.md mandate)· never weaken it to make a stress test pass.