Added MQTTStore.

Tests/MQTTStoreTests/MQTTStoreTests.swift

@@ -0,0 +1,77 @@
+import Logging
+import XCTest
+import MQTTNIO
+@testable import MQTTStore
+import NIO
+
+final class ServerTests: XCTestCase {
+  
+  func testConnect() throws {
+    let store = createTestStore()
+    _ = try store.connect(cleanSession: true).wait()
+    try store.destroy().wait()
+  }
+  
+  func testSubscriptionHandler() throws {
+    let store = createTestStore()
+    _ = try store.connectAndSubscribe(cleanSession: true).wait()
+    
+    _ = try store.client?.publish(
+      to: "test/topic",
+      payload: ByteBufferAllocator().buffer(string: "test"),
+      qos: .atLeastOnce
+    ).wait()
+    
+    Thread.sleep(forTimeInterval: 2)
+    
+    XCTAssertEqual(store.state.messages.count, 1)
+    XCTAssertEqual(store.state.messages[0], "test")
+    try store.destroy().wait()
+  }
+  
+  
+  func createTestStore() -> MQTTStore<TestState> {
+    .init(
+      state: .init(messages: []),
+      subscriptions: [("test/topic", stateHandler(_:_:))],
+      serverDetails: serverDetails,
+      eventLoopGroup: MultiThreadedEventLoopGroup.init(numberOfThreads: 1),
+      logger: logger
+    )
+  }
+  
+  let logger: Logger = {
+    var logger = Logger(label: "MQTT Test")
+    logger.logLevel = .trace
+    return logger
+  }()
+  
+  var serverDetails: ServerDetails {
+    .init(
+      identifier: "Test Server",
+      hostname: "localhost",
+      port: 1883,
+      version: .v3_1_1,
+      cleanSession: true,
+      useTLS: false,
+      useWebSocket: false,
+      webSocketUrl: "/mqtt",
+      username: nil,
+      password: nil
+    )
+  }
+  
+  struct TestState {
+    var messages: [String]
+  }
+  
+  func stateHandler(_ state: inout TestState, _ result: Result<MQTTPublishInfo, Error>) {
+    switch result {
+    case let .success(value):
+      let payload = String(buffer: value.payload)
+      state.messages.append(payload)
+    case .failure:
+      break
+    }
+  }
+}