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+# Test Project Split Design
+
+**Date:** 2026-03-12
+**Goal:** Split `NATS.Server.Tests` (609 files) into feature-focused test projects for developer ergonomics — easier to run just the tests for the subsystem you're working on.
+
+## Project Structure
+
+```
+tests/
+ NATS.Server.TestUtilities/ # Shared helpers, fixtures, parity tools (class library)
+ NATS.Server.Core.Tests/ # Client, server, parser, config, subscriptions, protocol
+ NATS.Server.Auth.Tests/ # Auth, accounts, permissions, JWT, NKeys
+ NATS.Server.JetStream.Tests/ # JetStream API, streams, consumers, storage, cluster
+ NATS.Server.Raft.Tests/ # RAFT consensus
+ NATS.Server.Clustering.Tests/ # Routes, cluster topology, inter-server protocol
+ NATS.Server.Gateways.Tests/ # Gateway connections, interest modes
+ NATS.Server.LeafNodes.Tests/ # Leaf node connections, hub-spoke
+ NATS.Server.Mqtt.Tests/ # MQTT protocol bridge
+ NATS.Server.Monitoring.Tests/ # Monitor endpoints, events, system events
+ NATS.Server.Transport.Tests/ # WebSocket, TLS, OCSP, IO
+ NATS.E2E.Tests/ # (existing, unchanged)
+```
+
+## TestUtilities Contents
+
+`NATS.Server.TestUtilities` is a **class library** (not a test project).
+
+### Shared helpers (deduplicated)
+- `TestPortAllocator` — `GetFreePort()` (currently duplicated in ~51 files)
+- `SocketTestHelper` — `ReadUntilAsync()`, raw socket connect/read patterns (~25 files)
+- `ServerTestHelper` — common server startup/teardown patterns
+
+### Shared fixtures
+- `JetStreamApiFixture` — moved from root (used by 52 JetStream test files)
+- `JetStreamClusterFixture` — consolidated from 2 duplicate definitions
+- `LeafFixture` — consolidated from 3 duplicate definitions
+
+### Parity utilities (non-test)
+- `NatsCapabilityInventory.cs`
+- `ParityRowInspector.cs`
+- `JetStreamParityTruthMatrix.cs`
+
+### TestData
+- `TestData/*.conf` files (copied to output directory)
+
+## File-to-Project Mapping
+
+### NATS.Server.Core.Tests (~75 files)
+
+**Root-level:**
+ClientClosedReasonTests, ClientFlagsTests, ClientHeaderTests, ClientKindCommandMatrixTests, ClientKindProtocolRoutingTests, ClientKindTests, ClientLifecycleTests, ClientProtocolParityTests, ClientPubSubTests, ClientServerGoParityTests, ClientSlowConsumerTests, ClientTests, ClientTraceModeTests, ClientTraceTests, ClientUnsubTests, ConfigIntegrationTests, ConfigProcessorTests, ConfigReloadTests, ConfigRuntimeParityTests, FlushCoalescingTests, IntegrationTests, InternalClientTests, LoggingTests, MessageTraceTests, MsgTraceGoParityTests, NatsConfLexerTests, NatsConfParserTests, NatsHeaderParserTests, NatsOptionsTests, NoRespondersTests, ParserTests, ResponseRoutingTests, ResponseTrackerTests, RttTests, ServerConfigTests, ServerStatsTests, ServerTests, SignalHandlerTests, SlopwatchSuppressAttribute, SlowConsumerStallGateTests, StallGateTests, SubjectMatchTests, SubjectTransformIntegrationTests, SubjectTransformTests, SubListTests, VerboseModeTests, WriteLoopTests, WriteTimeoutTests, ConcurrencyStressTests
+
+**Subfolders:** Configuration/ (14), Internal/ (8), IO/ (4), Protocol/ (7), Server/ (7), SubList/ (6), Subscriptions/ (6), Stress/ (3)
+
+**Parity test files (from Parity/ folder):** NatsStrictCapabilityInventoryTests, JetStreamParityTruthMatrixTests, GoParityRunnerTests, InfrastructureGoParityTests, DifferencesParityClosureTests
+
+### NATS.Server.Auth.Tests (~50 files)
+
+**Root-level:**
+AccountIsolationTests, AccountResolverTests, AccountStatsTests, AccountTests, AuthConfigTests, AuthIntegrationTests, AuthProtocolTests, AuthServiceTests, ClientPermissionsTests, JwtAuthenticatorTests, JwtTests, NKeyAuthenticatorTests, NKeyIntegrationTests, PermissionIntegrationTests, PermissionLruCacheTests, PermissionTemplateTests, SimpleUserPasswordAuthenticatorTests, TokenAuthenticatorTests, UserPasswordAuthenticatorTests, ImportExportTests
+
+**Subfolders:** Auth/ (25), Accounts/ (5)
+
+### NATS.Server.JetStream.Tests (~220 files)
+
+**Root-level:**
+All `JetStream*` files at root (~55), plus FileStoreTests, FileStoreEncryptionTests, MemStoreTests, StreamStoreContractTests, MirrorSourceRetryTests, ClusterJetStreamConfigProcessorTests
+
+**Subfolders:** JetStream/ and all sub-folders (163 files)
+
+### NATS.Server.Raft.Tests (~45 files)
+
+**Root-level:** RaftConsensusAdvancedParityTests, RaftElectionTests, RaftMembershipParityTests, RaftReplicationTests, RaftSafetyContractTests, RaftSnapshotCatchupTests, RaftSnapshotTransferParityTests, RaftTransportPersistenceTests
+
+**Subfolders:** Raft/ (36)
+
+### NATS.Server.Clustering.Tests (~30 files)
+
+**Root-level:** RouteHandshakeTests, RoutePoolTests, RouteRmsgForwardingTests, RouteSubscriptionPropagationTests, RouteWireSubscriptionProtocolTests, ImplicitDiscoveryTests, InterServerAccountProtocolTests
+
+**Subfolders:** Routes/ (21), Route/ (1)
+
+### NATS.Server.Gateways.Tests (~25 files)
+
+**Root-level:** GatewayAdvancedRemapRuntimeTests, GatewayAdvancedSemanticsTests, GatewayLeafBootstrapTests, GatewayProtocolTests
+
+**Subfolders:** Gateways/ (21)
+
+### NATS.Server.LeafNodes.Tests (~30 files)
+
+**Root-level:** LeafAdvancedSemanticsTests, LeafProtocolTests
+
+**Subfolders:** LeafNodes/ (26), LeafNode/ (1)
+
+### NATS.Server.Mqtt.Tests (~30 files)
+
+**Root-level:** MqttPersistenceTests
+
+**Subfolders:** Mqtt/ (28)
+
+### NATS.Server.Monitoring.Tests (~35 files)
+
+**Root-level:** EventSystemTests, JszMonitorTests, MonitorClusterEndpointTests, MonitorModelTests, MonitorTests, SubszTests, SystemEventsTests, SystemRequestReplyTests
+
+**Subfolders:** Monitoring/ (21), Events/ (10)
+
+### NATS.Server.Transport.Tests (~25 files)
+
+**Root-level:** OcspConfigTests, OcspStaplingTests, TlsConnectionWrapperTests, TlsHelperTests, TlsMapAuthenticatorTests, TlsOcspParityBatch1Tests, TlsOcspParityBatch2Tests, TlsRateLimiterTests, TlsServerTests
+
+**Subfolders:** WebSocket/ (15), Networking/ (1)
+
+## Project File Template
+
+Each test project follows the same base pattern:
+
+```xml
+
+
+ false
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+```
+
+**Project-specific package additions:**
+
+| Project | Extra packages |
+|---------|---------------|
+| Auth.Tests | `NATS.NKeys` |
+| JetStream.Tests | `NATS.Client.Core`, `JETSTREAM_INTEGRATION_MATRIX` define constant |
+| Transport.Tests | `Serilog.Sinks.File` (if TLS tests use it) |
+| Core.Tests | `NATS.Client.Core`, `Serilog.Sinks.File` |
+| Monitoring.Tests | `NATS.Client.Core` |
+
+**TestUtilities** is a plain class library:
+
+```xml
+
+
+ false
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+```
+
+## Migration Strategy
+
+### Phase 1: Create TestUtilities
+- Create `NATS.Server.TestUtilities` project
+- Extract `GetFreePort()`, `ReadUntilAsync()` into shared helper classes
+- Move `JetStreamApiFixture`, consolidated `JetStreamClusterFixture`, consolidated `LeafFixture`
+- Move parity utility files (non-test) and TestData
+- Update the original `NATS.Server.Tests` to reference TestUtilities
+- Verify build + all tests pass
+
+### Phase 2: Split projects one at a time (smallest first)
+1. Transport.Tests (~25 files)
+2. Mqtt.Tests (~30 files)
+3. Gateways.Tests (~25 files)
+4. LeafNodes.Tests (~30 files)
+5. Clustering.Tests (~30 files)
+6. Raft.Tests (~45 files)
+7. Monitoring.Tests (~35 files)
+8. Auth.Tests (~50 files)
+9. JetStream.Tests (~220 files)
+10. Core.Tests (rename remaining original project)
+
+Each step:
+- Create the new `.csproj`
+- Move files with `git mv` to preserve history
+- Update namespaces to match new project name
+- Add to solution file
+- Remove files from old project
+- Build + test
+
+### Phase 3: Cleanup
+- Delete the original `NATS.Server.Tests` project (now empty)
+- Verify `dotnet test` from solution root runs all projects
+- Verify CI still works
+
+## Decisions
+
+- **Namespaces updated** to match new project names (e.g., `NATS.Server.Auth.Tests`)
+- **Root-level files sorted** into matching subsystem projects by prefix/topic
+- **Storage files** (FileStore, MemStore, StreamStore) → JetStream project
+- **ImportExportTests** → Auth project
+- **InternalClientTests** → Core project
+- **Parity test files** → Core.Tests; parity utility classes → TestUtilities
+- **Stress test files** → Core.Tests (only 3-4 files, not worth a separate project)
+- **Trace files** → Core.Tests (tracing is a core feature)