Set baudrate, add mock serial struct to test with.

Tests/SwiftRPLidarTests/SwiftRPLidarTests.swift

@@ -13,3 +13,28 @@ final class SwiftRPLidarTests: XCTestCase {
         ("testExample", testExample),
     ]
 }
+
+struct MockSerialPort: LidarSerial {
+    
+    var dtr: Bool
+    
+    var inWaiting: Int
+    
+    func closePort() {
+    }
+    
+    func openPort() throws {
+    }
+    
+    func readData(ofLength: Int) throws -> Data {
+        return Data()
+    }
+    
+    func writeData(_ data: Data) throws -> Int {
+        return 0
+    }
+    
+    func setBaudrate(baudrate: Int) {
+        
+    }
+}