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End-to-End Tests

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Litho provides basic support for the Espresso UI Testing framework. For the time being, we only provide shallow selectors that will match ComponentHosts and LithoViews to run very high-level tests against. If you find that too limiting, please reach out to us and describe your use case.

Getting Started#

We ship with a bunch of custom matchers, which will hopefully make your life easier.

The matchers exist as their own litho-espresso package, so make sure to add the dependencies to your build.gradle file alongside your Espresso setup:



dependencies {
// ...
androidTestCompile 'com.facebook.litho:litho-espresso:0.40.0'
androidTestCompile 'com.android.support.test.espresso:espresso-core:2.2.2'
androidTestCompile 'com.android.support.test.espresso:espresso-intents:2.2.2'
}

Matching#

In order to instruct Litho to record where elements are mounted and give you access to testKeys you can set in your Components, replace your usual ActivityTestRule with the specialized LithoActivityTestRule:

@RunWith(AndroidJUnit4.class)
@LargeTest
public class MyTest {
@Rule
public LithoActivityTestRule<MyActivity> mActivity =
new LithoActivityTestRule<>(MyActivity.class);
// ...
}

Afterwards, you can check against ComponentHosts and LithoViews as you normally would for standard Android Views. For instance, let's assume you have a mounted clickable component like this present in the selected activity:

CustomButton.create(c)
.text("My Button")
.clickHandler(/* ... */)
.build();

Then, you could write an Espresso test like this:

@Test
public void testButtonIsDisplayedAndClickable() {
onView(ComponentHostMatchers.componentHostWithText(containsString("My Button")))
.check(matches(allOf(isDisplayed(), isClickable())));
}

Alternatively, you can match against components by using testKey. testKeys allow you to specify a string for a Component, similar to an Android viewTag, but without sacrificing view flattening. Instead, Litho maintains a separate data structure to keep track of the keys and associated metadata, but only if the end-to-end test mode is enabled through the use of LithoActivityTestRule:

CustomButton.create(c)
.text("My Button")
.testKey("my-button")
.clickHandler(/* ... */)
.build();
@Test
public void testButtonIsDisplayedAndClickableByTestKey() {
onView(LithoViewMatchers.withTestKey("my-button"))
.check(matches(allOf(isDisplayed(), isClickable())));
}

Next#

Either head back to the testing overview or continue with the next section, Running Tests in Android Studio.

Additional Resources#

There are plenty of additional matchers available, which you can look up in the API docs: