import re, unittest

class EmailExtractor:
    def __init__(self):
        pattern = "[a-z][a-zA-Z0-9_.-]+@[a-z]+\.[a-z]+$"
        self.c_pattern = re.compile(pattern)


    def isValidEmail(self, email):
        for email in  re.findall(self.c_pattern, email):
            return email
        return None


class EmailExtractorTest(unittest.TestCase):

    def main(self):
        email_extractor_obj = EmailExtractor()
        self.assertEqual(email_extractor_obj.isValidEmail("hello, I have added my email-address: testuser1@gmail.com"), "testuser1@gmail.com")
        self.assertEqual(email_extractor_obj.isValidEmail("hello, I have added my email-address: test1213@gmail.com"), "test1213@gmail.com")
        self.assertEqual(email_extractor_obj.isValidEmail("hello, I have added my email-address: 1testuser@gmail.com"), "testuser@gmail.com")
        self.assertEqual(email_extractor_obj.isValidEmail("hello, I have added my email-address: testuser@gmail"), None)
        self.assertEqual(email_extractor_obj.isValidEmail("hello, I have added my email-address: testuser@gmail."), None)
        self.assertEqual(email_extractor_obj.isValidEmail("hello, I have added my email-address: testuser@gmail.121"), None)


if __name__ == "__main__":
    EmailExtractorTest().main()