diff --git a/lib/com.js b/lib/com.js
index b83da7f..bc82a96 100644
--- a/lib/com.js
+++ b/lib/com.js
@@ -2,35 +2,34 @@
 
 const Emitter = require("events");
 
-function Mock(path, options, openCallback) {
-  this.isOpen = true;
-  this.baudRate = 0;
-  this.path = path;
-}
-
-Mock.prototype = Object.create(Emitter.prototype, {
-  constructor: {
-    value: Mock
+class SerialPort extends Emitter {
+  constructor(path, options, openCallback) {
+    super();
+    this.isOpen = true;
+    this.baudRate = 0;
+    this.path = path;
   }
-});
 
-Mock.prototype.write = function (buffer) {
-  // Tests are written to work with arrays not buffers
-  // this shouldn't impact the data, just the container
-  // This also should be changed in future test rewrites
-  if (Buffer.isBuffer(buffer)) {
-    buffer = Array.from(buffer);
-  }
+  write(buffer) {
+    // Tests are written to work with arrays not buffers
+    // this shouldn't impact the data, just the container
+    // This also should be changed in future test rewrites
+    /* istanbul ignore else */
+    if (Buffer.isBuffer(buffer)) {
+      buffer = Array.from(buffer);
+    }
 
-  this.lastWrite = buffer;
-  this.emit("write", buffer);
-};
+    this.lastWrite = buffer;
+    this.emit("write", buffer);
+  }
+}
 
 let com;
 let sp;
 let stub = {
-  SerialPort: Mock,
+  SerialPort,
   list() {
+    /* istanbul ignore next */
     return Promise.resolve([]);
   },
 };