Google Testing Blog: My main() Method Is Better Than Yours

My main() Method Is Better Than Yours

Monday, September 08, 2008

Miško Heverysrcpublic static void main(String[] args)
throws Exception {
// Creation Phase
Injector injector = Guice.createInjector(
new CalculatorServerModule(args));
Server server = injector.getInstance(Server.class);
// Run Phase
server.start();
}srcpublic static void main(String[] args)
throws Exception {
// Creation Phase
Server server = new ServerFactory(args)
.createServer();
// Run Phase
server.start();
}hereherehere

Notice how the creation-phase contains the code which builds the object graph of the application. The last line runs the application. The separation is very important. We can test the ServerFactory in isolation. Passing it different arguments and than asserting that the correct object graph got built. But, in order to do that the Factory class should do nothing but object graph construction. The object constructors better do nothing but field assignments. No reading of files, starting of threads, or any other work which would cause problems in unit-test. All we do is simply instantiate some graph of objects. The graph construction is controlled by the command line arguments which we passed into the constructor. So we can test creation-phase in isolation with unit-test. (Same applies for GUICE example)

The last line gets the application running. Here is where you can do all of your fun threads, file IO etc code. However, because the application is build from lots of objects collaborating together it is easy to test each object in isolation. In test I just instantiate the Server and pass in some test doubles in the constructor to mock out the not so interesting/hard to test code.

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My main() Method Is Better Than Yours

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