Rakesh,
Great questions especially about testing. First you can go to
http://developer.android.com/index.html and download the SDK and if you use Eclipse you can also the ADT plugin for Eclipse which greatly helps in development. There are also numerous examples at the site to help you get started. Or you could by Android in Action which walks you through getting setup, started, and developing real applications.
Now as for testing there are many different forms of testing as well as things like quality assurance. For the most basic forms of testing, unit testing (via
JUNIT), the Android ATP plugin for Eclipse has this built in so that you can exercise any application you develop. You can also use Android’s Emulator which comes with the SDK. The Emulator allows you to run virtual instances of Android so that you can test and debug your applications before you put them on a phone. Also you can put your application on your phone and test with little fear as long as you are not using the API to do things like delete files, change system settings, and the like. Generally if you get to that stage you want hardware you can test on that you do not mind if you accidentally overwrite all your contacts and such. Android also supports functional testing via JUNIT and others have integrated different testing frameworks with Android. Thus you can lets say have a database with various test data and then have your tests pull that data and exercise your application to perform functional testing. Furthermore you can use tools like Hudson,
Maven, Ant etc to integrate with the SDK and Emulator and even, automatically on a build server, kick of builds and tests in a continuous integration development environment to maintain quality in larger projects. In the case of testing security you can even integrate tools like Sulley to automatically perform fuzzing of applications or Android. As such more or less anything you want to do in the form of testing you can do on Android either in the emulator, or on a handset, and automate it to your hearts content.
Does that help?