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+# AppController Concurrency Test Design
+
+## Goal
+
+Verify that one singleton `AppController` instance remains correct under concurrent calls without requiring live MySQL, Redis, MQTT, or OSS services.
+
+## Scope
+
+Add a standalone unit concurrency test class covering three shared execution paths:
+
+1. `switchDevice`: 32 threads, 3,200 total calls. Validate every generated `startTime` as `yyyy-MM-dd HH:mm:ss`.
+2. `uploadImage`: 32 threads, 1,600 total calls across JPEG, PNG, GIF, WebP, and BMP. Validate each result and ensure no file type state leaks between calls.
+3. `editScheduleStatus`: 32 threads, 640 total calls. Give every call a unique schedule/device pair and validate that its MQTT payload contains only the matching device and schedule detail.
+
+## Concurrency Model
+
+Each test uses one fixed 32-thread executor and one shared controller instance. A ready latch ensures all workers are resident before a start latch releases them together. Every future has a bounded timeout so deadlocks and stalls fail the test instead of hanging the build.
+
+All service collaborators are preconfigured Mockito mocks. Login state required by schedule ownership checks is scoped independently in each worker thread.
+
+## Success Criteria
+
+- Every submitted operation completes within the timeout.
+- No malformed timestamps, image validation errors, payload contamination, deadlocks, or unexpected exceptions occur.
+- Invocation counts equal the requested operation totals.
+- Existing `water-app` tests remain green.
+
+## Non-goals
+
+- HTTP server throughput or latency benchmarking.
+- Database transaction contention testing.
+- Redis, MQTT broker, or OSS load testing.
+- Production code changes unless a concurrency defect is reproduced.