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[MUSIC]

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Up until now we've been
writing unit tests.

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But now,
we're going to be writing UI tests,

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which can also be called
instrumentation tests.

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The key difference is that a UI
test actually does run on a device.

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So, instead of using something like
Robolectric to help us pretend there's

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a device, we'll be running these tests
directly on an actual device or emulator.

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The upside is that when we see an error,

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we'll know that it happened
on an actual device.

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On the other hand, we now need
a device where we didn't before.

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There are pros and cons to each
of these methods of testing and

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it's up to you, the developer, to decide
which is the best way to test your app.

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For UI testing, we'll be using Espresso.

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Espresso is a testing framework
by Google included in

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the Android testing support library and
it makes it easy for

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us to automatically test
the functionality of our app.

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Let's get started with Espresso by
creating a new test class, but instead of

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creating it in the test package, we need
to create it in the androidTest package.

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If a test requires a device to run, then
it belongs in the androidTest package,

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if it doesn't require a device,
then we put it in the test package.

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Let's right click on
the androidTest package and

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create a new Java class
named MainActivityUITest.

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But before we get started with Espresso,
we'll need to add it as a dependency.

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Over in our build.gradle file,
let's add the necessary dependencies.

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You can copy them in from
the teacher's notes below.

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We also need to add a line to
the defaultConfig section.

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Let's copy and paste that in from
the teacher's notes as well.

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Then let's sync the project.

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And we're good to go.

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Back in MainActivityUITest,

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let's tell Android Studio which runner
to use by adding a run with annotation

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above our class, @RunWith,

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and then passing in AndroidJUnit4.class.

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Next we need to tell Espresso
which activity we'll be testing.

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This is done by using a special rule
from the Android support library,

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called activity test rule.

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Inside our class, let's create
a new activity test rule field

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starting with the rule annotation, @Rule.

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Then on the next line,
let's add public_ActivityTestRule.

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And inside the angle brackets,
let's specify our activity, MainActivity.

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Then let's name our field
activityTestRule and

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set it equal to new ActivityTestRule.

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Then we just need to pass
in MainActivity.class,

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add a semicolon, and we're done.

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Also, if we hover our cursor
over the gray MainActivity,

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it looks like it's unnecessary.

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Let's use Alt+Enter to get rid of it.

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Now that we've got our rules set up, we're
ready to start testing with Espresso, but

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since this is our third round of testing,
instead of writing out everything,

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let's skip ahead to the important bits by
copying in the three test methods from

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the teacher's notes below.

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And let's use Alt+Enter
to import the test class.

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In the next video, will kick off our
Espresso testing by testing our edit text.