Unit tests for https://stackoverflow.com/q/70752266/3141234

letter_pattern.py

def letterPattern(size):
    # TODO: your code goes here
    result = ""
    for i in range(size):
        p = 65
        
        for j in range(i, size):
            result += chr(p)
            p += 1
            
        result += "\n"
        
    return result

def main():
    print("What size of pattern would you like?")
    size = int(input())
    pattern = letterPattern(size)
    print(pattern)

import sys
import unittest
import inspect

class TestLetterPattern(unittest.TestCase):
    def test_input_0(self):
        self.assertEqual(letterPattern(0), "")
        
    def test_input_1(self):
        self.assertEqual(letterPattern(1), "AA")
        
    def test_input_2(self):
        expected =  inspect.cleandoc("""\
        ABBA
        A  A
        """)
        self.assertEqual(letterPattern(2), expected)
        
    def test_input_3(self):
        expected = inspect.cleandoc("""\
        ABCCBA
        AB  BA
        A    A
        """)
        self.assertEqual(letterPattern(3), expected)
        
    def test_input_4(self):
        expected = inspect.cleandoc("""\
        ABCDDCBA
        ABC  CBA
        AB    BA
        A      A
        """)
        self.assertEqual(letterPattern(4), expected)
        
    def test_input_7(self):
        expected = inspect.cleandoc("""\
        ABCDEFGGFEDCBA
        ABCDEF  FEDCBA
        ABCDE    EDCBA
        ABCD      DCBA
        ABC        CBA
        AB          BA
        A            A
        """)
        self.assertEqual(letterPattern(7), expected)
        
    def test_input_26(self):
        expected = inspect.cleandoc("""\
        ABCDEFGHIJKLMNOPQRSTUVWXYZZYXWVUTSRQPONMLKJIHGFEDCBA
        ABCDEFGHIJKLMNOPQRSTUVWXY  YXWVUTSRQPONMLKJIHGFEDCBA
        ABCDEFGHIJKLMNOPQRSTUVWX    XWVUTSRQPONMLKJIHGFEDCBA
        ABCDEFGHIJKLMNOPQRSTUVW      WVUTSRQPONMLKJIHGFEDCBA
        ABCDEFGHIJKLMNOPQRSTUV        VUTSRQPONMLKJIHGFEDCBA
        ABCDEFGHIJKLMNOPQRSTU          UTSRQPONMLKJIHGFEDCBA
        ABCDEFGHIJKLMNOPQRST            TSRQPONMLKJIHGFEDCBA
        ABCDEFGHIJKLMNOPQRS              SRQPONMLKJIHGFEDCBA
        ABCDEFGHIJKLMNOPQR                RQPONMLKJIHGFEDCBA
        ABCDEFGHIJKLMNOPQ                  QPONMLKJIHGFEDCBA
        ABCDEFGHIJKLMNOP                    PONMLKJIHGFEDCBA
        ABCDEFGHIJKLMNO                      ONMLKJIHGFEDCBA
        ABCDEFGHIJKLMN                        NMLKJIHGFEDCBA
        ABCDEFGHIJKLM                          MLKJIHGFEDCBA
        ABCDEFGHIJKL                            LKJIHGFEDCBA
        ABCDEFGHIJK                              KJIHGFEDCBA
        ABCDEFGHIJ                                JIHGFEDCBA
        ABCDEFGHI                                  IHGFEDCBA
        ABCDEFGH                                    HGFEDCBA
        ABCDEFG                                      GFEDCBA
        ABCDEF                                        FEDCBA
        ABCDE                                          EDCBA
        ABCD                                            DCBA
        ABC                                              CBA
        AB                                                BA
        A                                                  A
        """)
        self.assertEqual(letterPattern(26), expected)
        
if __name__ == '__main__':
    if len(sys.argv) == 2 and sys.argv[1] == "--test":
        argv_for_unit_test = sys.argv.copy()
        argv_for_unit_test.pop(1) # Remove the "--test" flag
        unittest.main(argv = argv_for_unit_test)
    else:
        main()

When you call this like python3 letter_pattern.py, it will prompt you for the size of the pattern you want interactively.

If you instead run it with python3 letter_pattern.py --test, it will automatically test the patterns of size 0, 1, 2, 3, 4, 7 and 26.