import unittest
from unittest.mock import patch
from io import StringIO

# Import our program
import hello_world as hw

class TestHelloClass(unittest.TestCase):

    @patch('sys.stdout', new_callable = StringIO)
    def test_main(self, stdout):

        # Test main()
        hw.main()
        extected_out = 'main() is called\n'

        # Check stdout
        self.assertEqual(stdout.getvalue(), extected_out)


    # The order of decorator is important!
    @patch('sys.stdout', new_callable = StringIO)
    @patch('sys.stderr', new_callable = StringIO)
    def test_constructor(self, stderr, stdout):

        # Test empty string passed to HelloClass contructor
        hc = hw.HelloClass('')
        hc.hello()

        # Expect a warning message to stderr
        expected_err = 'Warning: empty string!\n'
        
        # Expect an empty string used as name
        expected_out = 'Hi, \n'

        # Check stdout and stderr
        self.assertEqual(stdout.getvalue(), expected_out)
        self.assertEqual(stderr.getvalue(), expected_err)


    # Note that no argument is passed to function after patching sys.stdin
    @patch('sys.stdin', StringIO('Bob\n'))
    @patch('sys.stdout', new_callable = StringIO)
    def test_change_name(self, stdout):

        # Initial class
        hc = hw.HelloClass('John')

        hc.hello()  # Hi, John
        hc.update_name()
        hc.hello()  # Hi, Bob

        expected_out = """Hi, John
Your new name: You have changed your name!
Hi, Bob
"""
        self.assertEqual(stdout.getvalue(), expected_out)

if __name__ == '__main__':
    unittest.main()