third.py

# Write unittests for this function:

import unittest


def count_letter_in_string(string, letter):
    if type(string) != str:
        return 0
    count = 0
    for current_letter in string:
        if current_letter == letter:
            count += 1
    return count


class TestForExerciseThird(unittest.TestCase):

    def test_CheckNormalWorking(self):
        self.assertEqual(count_letter_in_string('almafa alatt alszik az alma', 'a'), 9)

    def test_CheckFirstInputNotString(self):
        self.assertEqual(count_letter_in_string(12345, 'a'), 0)

    def test_CheckSecondInputNotString(self):
        self.assertEqual(count_letter_in_string('almafa alatt alszik az alma', 5), 0)

    def test_CheckGivenEmptyStringInput(self):
        self.assertEqual(count_letter_in_string('', 'a'), 0)

    def test_CheckGivenSecondInputAsList(self):
        self.assertEqual(count_letter_in_string('almafa alatt alszik az alma', ['a', 'b']), 0)


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