要检查键盘是否隐藏，可以使用Android的InputMethodManager类的isAcceptingText()方法。

以下是一个使用Espresso进行UI测试的示例代码：

import android.app.Activity;
import android.content.Context;
import android.view.View;
import android.view.inputmethod.InputMethodManager;

import androidx.test.espresso.UiController;
import androidx.test.espresso.ViewAction;
import androidx.test.espresso.matcher.ViewMatchers;
import androidx.test.rule.ActivityTestRule;
import androidx.test.runner.AndroidJUnit4;

import org.hamcrest.Matcher;
import org.junit.Rule;
import org.junit.Test;
import org.junit.runner.RunWith;

import static androidx.test.espresso.Espresso.onView;
import static androidx.test.espresso.action.ViewActions.click;
import static androidx.test.espresso.action.ViewActions.closeSoftKeyboard;
import static androidx.test.espresso.action.ViewActions.typeText;
import static androidx.test.espresso.assertion.ViewAssertions.matches;
import static androidx.test.espresso.matcher.ViewMatchers.isDisplayed;
import static org.hamcrest.Matchers.not;

@RunWith(AndroidJUnit4.class)
public class KeyboardTest {

    @Rule
    public ActivityTestRule activityRule = new ActivityTestRule<>(MainActivity.class);

    @Test
    public void testKeyboardHidden() {
        onView(ViewMatchers.withId(R.id.editText)).perform(typeText("Test"), closeSoftKeyboard());
        onView(ViewMatchers.withId(R.id.button)).perform(click());

        onView(ViewMatchers.withId(R.id.editText)).check(matches(not(isKeyboardShown())));
    }

    private static Matcher isKeyboardShown() {
        return new Matcher() {
            @Override
            public boolean matches(Object item) {
                if (item instanceof View) {
                    View view = (View) item;
                    InputMethodManager imm = (InputMethodManager) view.getContext().getSystemService(Context.INPUT_METHOD_SERVICE);
                    return imm.isAcceptingText();
                }
                return false;
            }

            @Override
            public void describeMismatch(Object item, Description mismatchDescription) {
                mismatchDescription.appendText("Keyboard is shown");
            }

            @Override
            public void _dont_implement_Matcher___instead_extend_BaseMatcher_() {

            }

            @Override
            public void describeTo(Description description) {
                description.appendText("Keyboard is hidden");
            }
        };
    }
}

在上面的示例中，我们首先在EditText上输入一些文本，然后关闭键盘。然后，我们点击一个按钮触发一些操作。最后，我们使用自定义的isKeyboardShown()方法来检查键盘是否隐藏，然后使用Espresso的matches()方法进行断言。如果键盘隐藏，断言将成功通过。