Create custom Espresso matchers

This article describes customizing Espresso's matchers through BoundedMatcher.

Overview

Android provides the BoundedMatcher class for creating View-specific Espresso matchers.

For details, please go to: https://developer.android.com/training/testing/espresso/lists.html

Example

Here is a custom matcher for checking EditText hint text:

First you need to create the Matchers class in the src/androidTest/java directory.

/**
 * Created by lulu on 2018/3/10.
 * 自定义的 View 匹配器
 */
public class Matchers {
    public static Matcher<View> withItemHint(final String itemHintText) {
        checkArgument(!(itemHintText.equals(null)));
        return withItemHint(is(itemHintText));
    }
    public static Matcher<View> withItemHint(final Matcher<String> matcherText) {
        // 如果传入非法的 matcher 需提前处理
        checkNotNull(matcherText);
        return new BoundedMatcher<View, EditText>(EditText.class) {

            @Override
            public void describeTo(Description description) {
                description.appendText("该 EditText 的 Hint 为: " + matcherText);
            }

            @Override
            protected boolean matchesSafely(EditText item) {
                return matcherText.matches(item.getHint().toString());
            }
        };
    }
}

Use the Matchers class you just created with the following code.

// more
import static com.lulu.androidtestdemo.espresso.custom_matcher.Matchers.withItemHint;

/**
 * Created by lulu on 2018/3/10.
 * 测试自定义匹配器
 */
@RunWith(AndroidJUnit4.class)
public class TestCustomMatcher {

    @Rule
    public ActivityTestRule<EspressoTest1Activity> mRule =
            new ActivityTestRule<EspressoTest1Activity>(EspressoTest1Activity.class);

    @Test
    public void testEditHintDisplay() throws Exception {
        onView(withId(R.id.inputField)).check(matches(withItemHint("this is a hint")));
    }
}