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Page Object Pattern

The page object pattern is a very popular design pattern when writing automation tests helping minimize code duplication and test code that is easy to maintain.

What is a page object

A page object is an object oriented class that is an abstraction over the user interface for an automation test.

How to make a page object

Quote

The basic rule of thumb for a page object is that it should allow a software client to do anything and see anything that a human can. It should also provide an interface that's easy to program to and hides the underlying widgetry in the window.

-Martin Fowler

Using the rule above, what might be some objects that a user could interact with on each page below?

LoginPage LoggedInPage
Answer

LoginPage

  • email
  • password
  • sign in or register button

LoggedInPage

  • profile image
  • greeting text

BasePage

To start building these page objects, first define an interface that will provide one simple function to assert the screen is visible. This will be essential for the navigation DSL later. 

interface BasePage {

    fun assertScreen()

}

The rest of the page objects may be implemented using the BasePage. Since Espresso is being used to write the tests, every object on each page shall return a ViewInteraction to provide tests an interface for interacting with views.

LoginPage

class LoginPage : BasePage {

    override fun assertScreen() = TODO()

    fun onEmail(): ViewInteraction = TODO()
    fun onPassword(): ViewInteraction = TODO()
    fun onSignInOrRegisterButton(): ViewInteraction = TODO()

}

LoggedInPage

class LoggedInPage : BasePage {

    override fun assertScreen() = TODO()

    fun onWelcomeGreeting(): ViewInteraction = TODO()
    fun onProfileImage(): ViewInteraction = TODO()

}

Simple Test

With each page object defined, a successful login test can be written using some Espresso ViewActions to type in the login info and verify the user name after a successful submission. 

@Test 
fun successfulLogin() {
    val scenario = ActivityScenario.launch(LoginActivity::class.java)

    LoginPage().apply {
        onEmail().perform(ViewActions.typeText("andrew@test.com"))
        onPassword().perform(ViewActions.typeText("password123"))
        onSignInOrRegisterButton().perform(ViewActions.click())
    }

    LoggedInPage().onWelcomeGreeting().check(matches(withText("Welcome Andrew!")))

}

As you probably have noticed, none of the functions in the page object have been implemented and the test above is a little verbose. Move onto the next section to learn about some helpful extension functions that simplify implementing the rest of the page object and make the test more expressive.

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