Ionic application is developed using AngularJS. AngularJS has a collection of test libraries and frameworks such as Karma, Jasmine test runner, etc. Ionic uses these frameworks for testing of an application.
There are four WAYS to test Ionic App: in a desktop WebKit browser, in the iOS or Android simulator, in a mobile browser on your phone, or as a native app on the phone.
Desktop browser testing:

Testing your app in a browser is as simple as running the server command.

                                $ ionic serve

This will start a live-reload server for your project. When changes are made to any HTML, CSS, or JavaScript FILES, the browser will automatically reload when the files are saved.

• Simulator Testing:

We can also test in the simulator using cordova commands. For eg: to test in IOS simulator, run:
                                       $ ionic cordova build ios
                                       $ ionic cordova emulate ios
Whereas in Android testing, If you want to get advanced, you can also open up the project file for a specific platform by opening the required Xcode or Android Eclipse project in platforms inside the root of your project. Then, you can build and test the platform-specific IDE.

• Mobile browser testing:

We can also test the app directly in a mobile browser. For OS X users, Safari on OS X can debug websites and simulator applications. First, we have to enable the remote web inspector on both the device and Safari on the desktop. To do this with iOS 7 and OS X Mavericks, enable Web Inspector option in the iOS Settings -> Safari -> Advanced section, and also enable the Developer Menu in the Advanced section of Safari OS X settings.
Android apps supporting Android 4.4 or above can use Chrome for remote debugging.
If you are using the local server method from the Desktop testing section and you are on the same network as a desktop computer, you can connect to the IP address of the desktop computer to test. So, if our desktop is running a test server at 192.168.1.123:8000, we can just load that address into our mobile Chrome or Safari to test it.

One problem testing in a mobile browser is that it’s probably the furthest of the three options from the actual app experience. This is largely because the browser app is for browsing websites, so it often adds functionality that conflicts with your app. For example, Chrome and Safari both listen for drag events on the sides of the app which allows switching between open tabs. They have issues with the URL bars getting in the way, and some scrolling behavior is not the same as it is in the web view running in Cordova. It is FINE for small tests, but definitely not RECOMMENDED for more complex apps.

• Testing as a native app:

Since we are building a native app, we can test it. There are several ways to do this. If you are building for iOS devices, you’ll need to sign up for an Apple Developer account to test as a native app on an iPhone or iPad. Once you have an account and you need to have set up Xcode with your certificates to enable device testing, you’ll want to open the Xcode project from platforms/ios/ and do your testing from Xcode. Testing on Android is much easier and faster. To test on a device, simply plug it in and run.
                                   $ ionic cordova run android
If this doesn’t work, make sure you have USB debugging enabled on your android device.