When setting out the components within a project's UI code (as illustrated in the gui sub-package), care should be taken to define types and classes that have a single responsibility and a clear API. Doing so will make it easier to load and test individual components with the standard Go testing tools. If smaller components can be tested, we we can avoid launching the whole application and the required test runners, therefore making the testing process much faster. When a test suite runs quickly, it can be run more frequently and extended more easily, leading to higher test coverage and greater confidence in the software quality.

For a practical example, let's look at the GoMail compose dialog and its Send button. Clearly, the dialog box should perform all sorts of validation before sending, and if they pass then send the email. Validation can easily be tested with normal unit tests, but verifying that the send button correctly sends a new email will require the user interface to be tested. In the following example, we will load the compose window, enter some data, and simulate the Send button being pressed. By using a test email server, as used through each of the GoMail examples, we can check that the email has been sent by the user interface without needing to communicate with a real email server.