Assert exceptions in Android Espresso test

问题

I have a test in Espresso that needs to assert that a certain action cause an exception to be thrown.

However it seems that the Espresso framework swallows the original exception and only surfaces a PerformException.

回答1:

Eventually I found a way to do it. I've created a custom Hamcrest matcher that allows you to verify a nested exception.

public class NestedExceptionMatcher extends TypeSafeMatcher<Throwable> {

    private final Class<?> mExpectedType;
    private final Matcher<String> mMessageMatcher;

    static NestedExceptionMatcher expectNestedThrowable(Class<?> expectedType, Matcher<String> messageMatcher) {
        return new NestedExceptionMatcher(expectedType, messageMatcher);
    }

    NestedExceptionMatcher(Class<?> expectedType, Matcher<String> messageMatcher) {
        mExpectedType = expectedType;
        mMessageMatcher = messageMatcher;
    }

    @Override
    protected boolean matchesSafely(Throwable item) {
        boolean matches = isMatch(item);

        Throwable currentThrowable = item.getCause();
        while (!matches && currentThrowable != null) {
            matches = isMatch(currentThrowable);
            currentThrowable = currentThrowable.getCause();
        }

        return matches;
    }

    @Override
    public void describeTo(Description description) {
        description
                .appendText("expects type ")
                .appendValue(mExpectedType)
                .appendText(" with a message ")
                .appendDescriptionOf(mMessageMatcher);
    }

    private boolean isMatch(Throwable t) {
        return t.getClass().isAssignableFrom(mExpectedType) && mMessageMatcher.matches(t.getMessage());
    }
}

And then you can use it as follows in your test:

public class SomeActivityTest {

    @Rule
    public ActivityTestRule<SomeActivity> mRule = new ActivityTestRule<>(
            SomeActivity.class, false, false);

    @Rule
    public ExpectedException mExceptionRule = ExpectedException.none();

    @Test
    public void testClick_whenInvalidParamsAreSet_shouldThrowException() {
        mRule.launchActivity(getIntentWithInvalidParams());
        mExceptionRule.expect(expectNestedThrowable(
                IllegalArgumentException.class,
                containsString("parameter isn't defined")
        ));

        onView(withId(R.id.my_btn)).perform(click());
    }

    private Intent getIntentWithInvalidParams() {
        ...
    }
}

回答2:

You can do this

@Test( expected = ArrayIndexOutOfBoundsException.class) //OR any other  
throwable
public void myTest() {

}

回答3:

Why not use this:

 @Test(expected = PerformException::class)
    fun traderSummaryContainer_notScroll() {
        onView(withId(R.id.traderSummaryContainer))
                .perform(scrollTo())
    }

回答4:

Use normal try catch solved my problem, i know the exception is nested. But we can still check it by cause:

    var error: Throwable? = null
    try {
        onView(something).perform(click())
    } catch (e: Throwable) {
        error = e;
    }
    assert(error!!.cause is MySpecificException)
    assert(error!!.cause!!.message == "My specific error message")

I have tried the above custom Hamcrest matcher approach, but i ended up having flaky tests, so moved into this one eventually.

来源：https://stackoverflow.com/questions/50563600/assert-exceptions-in-android-espresso-test

标签

android

unit-testing

android-espresso