Verify AlertDialog shown on invalid text input

I am writing tests for an android application by using ActivityInstrumentationTestCase2. And I would like to verify that an AlertDialog is shown when the input for an EditText is invalid.

The documentation says:

You can also verify that the Activity responds to invalid input by sett开发者_运维技巧ing error messages in the View.

http://androidappdocs.appspot.com/guide/topics/testing/activity_testing.html

I think this is what I need. But I can't find how. How can I do this?

Ok I found a solution.

First of all I downloaded Robotium.

After that I checked whether the AlertDialog is shown by checking the text it contains:

    public void testEnterNumberEditBoxForInvalidNumber() {
    solo.enterText(0, "1234567890123456");
    solo.clickOnImageButton(0);
    boolean actual = solo.searchText("The number entered is not valid.");

    assertEquals(true, actual);

}

I'm open to better solutions. That's why I won't mark the question checked for a while.