Update vid/pid check in usbDetect.find(...) to check for function callback

index.js

@@ -3,6 +3,10 @@
 
 var index = require('./package.json');
 
+function isFunction(functionToCheck) {
+	return typeof functionToCheck === 'function';
+}
+
 if(global[index.name] && global[index.name].version === index.version) {
 	module.exports = global[index.name];
 } else {
@@ -18,16 +22,14 @@ if(global[index.name] && global[index.name].version === index.version) {
 	//detector.find = detection.find;
 	detector.find = function(vid, pid, callback) {
 		// Suss out the optional parameters
-		if(!pid && !callback) {
+		if(isFunction(vid) && !pid && !callback) {
 			callback = vid;
 			vid = undefined;
-		}
-		else if(!callback) {
+		} else if(isFunction(pid) && !callback) {
 			callback = pid;
 			pid = undefined;
 		}
 
-
 		return new Promise(function(resolve, reject) {
 			// Assemble the optional args into something we can use with `apply`
 			var args = [];

test/test.js

@@ -11,12 +11,14 @@ var getSetTimeoutPromise = require('./lib/set-timeout-promise-helper');
 var usbDetect = require('../');
 
 const MANUAL_INTERACTION_TIMEOUT = 10000;
+const USB_TEST_VID = process.env.TEST_VID || 5824; // VID of the tevice used to test
+const USB_TEST_PID = process.env.TEST_PID || 1155;
 
 // We just look at the keys of this device object
 var DEVICE_OBJECT_FIXTURE = {
 	locationId: 0,
-	vendorId: 5824,
-	productId: 1155,
+	vendorId: USB_TEST_VID,
+	productId: USB_TEST_PID,
 	deviceName: 'Teensy USB Serial (COM3)',
 	manufacturer: 'PJRC.COM, LLC.',
 	serialNumber: '',
@@ -63,6 +65,27 @@ describe('usb-detection', function() {
 				});
 			});
 
+			it('should return a promise when vid and pid are given', async function(done) {
+				const devices = await usbDetect.find();
+				usbDetect.find(devices[0].vendorId, devices[0].productId)
+					.then(function(devices) {
+						testArrayOfDevicesShape(devices);
+					})
+					.then(done)
+					.catch(done.fail);
+			});
+
+			it('should return a promise when vid is given', async function(done) {
+				const devices = await usbDetect.find();
+				usbDetect.find(devices[0].vendorId)
+					.then(function(devices) {
+						testArrayOfDevicesShape(devices);
+					})
+					.then(done)
+					.catch(done.fail);
+			});
+
+
 			it('should return a promise', function(done) {
 				usbDetect.find()
 					.then(function(devices) {