I'm getting an error "No Apex class named 'AnimalLocatorMock' was found" when validating the challenge.  However, everything seems to be coded correctly, and I have 100 percent code coverage on the AnimalLocator class.  I have no idea what's wrong with my test classes.  Does anyone have any ideas about what code be wrong?

@IsTest
private class AnimalLocatorTest {
    @isTest static  void  testGetCallout() {
    // Set mock callout class
    Test.setMock(HttpCalloutMock.class, new AnimalLocatorMock());
    // This causes a fake response to be sent
    // from the class that implements HttpCalloutMock.
    String animalname = AnimalLocator.getAnimalNameById(2);
    // Verify that the response received contains fake values        
    String expectedValue = 'bear';
    System.assertEquals(animalname, expectedValue);
    }
}

@IsTest
global class AnimalLocatorMock implements HttpCalloutMock {
    //Implement this interface method
    global HTTPResponse respond(HTTPRequest request) {
        // Create a fake response
        HttpResponse response = new HttpResponse();
        response.setHeader('Content-Type', 'application/json');
        response.setBody('{"animal":{"id":2,"name":"bear","eats":"berries, campers, adam seligman","says":"yum yum"}}');
        response.setStatusCode(200);
        return response;
    }
}