Test-Driven Development in Android MVVM Architecture(Part 3-Espresso)

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Espresso is an open-source android user interface (UI) testing framework developed by Google.

What is Espresso?

Espresso is a simple, efficient, and flexible testing framework. Here, we gonna setup the Espresso framework in a project, the workflow of the framework, and finding, automating & asserting user interface components in the testing environment with the simple android application.

Espresso basically has 3 components

• ViewMatchers — allows finding view in the current view hierarchy
• ViewActions — allows performing actions on the views
• ViewAssertions — allows asserting the state of a view

Outline Structure:
onView(ViewMatcher)         
.perform(ViewAction)
.check(ViewAssertion)

Before begin, if you didn’t check with my previous article, I recommend you check it here.

We have a small sample android application that hosts a Login screen and Home screen. You can clone it here. I recommend you clone this repo and checkout to tdd-unit-testing branch, so you can easily understand the flow ✌.

shehzabdeveloper/Test_Driven_Development

git clone https://github.com/shehzab.developer/Test_Driven_Development.git

git checkout -b tdd-unit-testing

Let’s start step by step…

Step 1: Add below dependencies into your app module’s build.gradle.
Espresso support:
androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'
Espresso intent mocking support:
androidTestImplementation 'androidx.test.espresso:espresso-intents:3.2.0'
ActivityTestRule:
androidTestImplementation 'androidx.test:rules:1.2.0'

Step 2: Its recommended to turn off animations in the android device which is used for testing.

Step 3: Open your project, goto package login, open LoginActivity.kt.

Step 4: Right-click LoginActivity.kt and select Generate > test

Right-click LoginViewModel and select Generate

Select Test…

Step 5: Pop-up appears. Select default values (cross-check with this image -left side) and click Ok.

Step 6: Pop-up appears. Select an androidTest and click Ok.

Notice the generated LoginActivityTest class in androidTest/login/ package.

Step 7: Now we need to add @RunWith(AndroidJunit4::class) on class name and ActivityTestRule which provides functional testing of single Activity.

So now code looks like:

@RunWith(AndroidJUnit4::class)
class LoginActivityTest{
    @get:Rule
    var activityTestRule = ActivityTestRule(LoginActivity::class.java)
    
}

Step 8: Now we ill write a simple test case to check whether username edit text is visible or not.
Write a method named as isUsernameEditTextDislayed with @Test annotation. Copy-paste below code snippet.

@Test
fun isUsernameEditTextDisplayed() {
    activityTestRule.launchActivity(Intent())
    onView(withId(R.id.etUsername)).check(matches(isDisplayed()))
}

In the above code, I am calling username edit text Id inside ViewMatcher and checking is it visible or not with ViewAssertion.
Run the test. Cool… It passed. For the running test, we need a physical device or emulator.

Espresso methods can be self-explanatory.

Step 9: Now we ill write test cases for a user entering username and password and click on the Login button. Followed by HomeActivity opens.

@Test
fun isUserLoggedAndHomeScreenCalled() {
    activityTestRule.launchActivity(Intent())
    
    //entering username
    onView(withId(R.id.etUsername)).perform(
        ViewActions.typeText("android"),
        ViewActions.closeSoftKeyboard()
    )
    
    //entering password
    onView(withId(R.id.etPassword)).perform(
        ViewActions.typeText("123456"),
        ViewActions.closeSoftKeyboard()
    )
    //checking  HomeActivity is called
    Intents.init()
    onView(withId(R.id.btnLogin)).perform(ViewActions.click())
    Intents.intended(IntentMatchers.hasComponent(HomeActivity::class.java.name))
    Intents.release()
}

Run the test. Cool… It passed ✌.

Awesome 👏👏👏. We just completed the basic intro to testing. Don’t stop here there is more to learn.

For complete source code for this chapter, checkout repo to tdd-espresso.
git checkout -b tdd-espresso

Thank you for your time to read this article. If you like it please give me your clap 👏 , so others can find it too.