Update persistent session tests

Tests/MQTTNIOTests/MQTTNIOTests.swift

@@ -451,7 +451,6 @@ final class MQTTNIOTests: XCTestCase {
                 XCTFail("\(error)")
             }
         }
-        _ = try client2.connect(cleanSession: true).wait()
         _ = try client2.connect(cleanSession: false).wait()
         _ = try client2.subscribe(to: [.init(topicFilter: "testPersistentAtLeastOnce", qos: .atLeastOnce)]).wait()
         try client.publish(to: "testPersistentAtLeastOnce", payload: payload, qos: .atLeastOnce).wait()
@@ -461,11 +460,49 @@ final class MQTTNIOTests: XCTestCase {
         // client2 should receive this publish as we have reconnected with clean session set to false
         try client.publish(to: "testPersistentAtLeastOnce", payload: payload, qos: .atLeastOnce).wait()
         Thread.sleep(forTimeInterval: 1)
+
+        wait(for: [expectation], timeout: 5.0)
+
+        try client.disconnect().wait()
+        try client2.disconnect().wait()
+    }
+
+    func testNonPersistentSession() throws {
+        let expectation = XCTestExpectation(description: "testPersistentSession")
+        expectation.expectedFulfillmentCount = 1
+        expectation.assertForOverFulfill = true
+
+        let payloadString = #"{"from":1000000,"to":1234567,"type":1,"content":"I am a beginner in swift and I am studying hard!!测试\n\n test, message","timestamp":1607243024,"nonce":"pAx2EsUuXrVuiIU3GGOGHNbUjzRRdT5b","sign":"ff902e31a6a5f5343d70a3a93ac9f946adf1caccab539c6f3a6"}"#
+        let payload = ByteBufferAllocator().buffer(string: payloadString)
+
+        let client = self.createClient(identifier: "testPersistentSession_publisher")
+        defer { XCTAssertNoThrow(try client.syncShutdownGracefully()) }
+        _ = try client.connect().wait()
+        let client2 = self.createClient(identifier: "testPersistentSession_subscriber")
+        defer { XCTAssertNoThrow(try client2.syncShutdownGracefully()) }
+
+        client2.addPublishListener(named: "test") { result in
+            switch result {
+            case .success(let publish):
+                var buffer = publish.payload
+                let string = buffer.readString(length: buffer.readableBytes)
+                XCTAssertEqual(string, payloadString)
+                expectation.fulfill()
+
+            case .failure(let error):
+                XCTFail("\(error)")
+            }
+        }
+        _ = try client2.connect(cleanSession: false).wait()
+        _ = try client2.subscribe(to: [.init(topicFilter: "testPersistentAtLeastOnce", qos: .atLeastOnce)]).wait()
+        try client.publish(to: "testPersistentAtLeastOnce", payload: payload, qos: .atLeastOnce).wait()
+        Thread.sleep(forTimeInterval: 1)
+        // disconnect and reconnect with clean session
         try client2.disconnect().wait()
-        // should not receive previous publish on connect as this is a cleanSession
         _ = try client2.connect(cleanSession: true).wait()
         // client2 should not receive this publish as we have reconnected with clean session set to true
         try client.publish(to: "testPersistentAtLeastOnce", payload: payload, qos: .atLeastOnce).wait()
+        Thread.sleep(forTimeInterval: 1)
 
         wait(for: [expectation], timeout: 5.0)