Justification (input string 'abc')
----------------------------------
ljust: 'abc'
ljust: 'abc'
ljust: 'abc  '
ljust: 'abc--'
rjust: 'abc'
rjust: 'abc'
rjust: '  abc'
rjust: '--abc'
zfill: 'abc'
zfill: 'abc'
zfill: '00abc'

Content checking
----------------
is_num abc   : 0
is_num 123   : 1
is_alpha ab  : 1
is_alpha 1a  : 0
is_alpha a1  : 0
is_alnum ab  : 1
is_alnum 1a  : 1
is_alnum a1  : 1
is_alnum 12  : 1
is_alnum ##12: 0

String counting (input str 'aabbaa')
------------------------------------
count_substr aa: 2
count_substr bb: 1
count_substr cc: 0

Starts/endswith
---------------
starts_with bro: 1
starts_with ids: 0
ends_with ids: 1
ends_with bro: 0

Transformations
---------------
swap_case 'aBc': AbC
to_title 'bro is a very neat ids': 'Bro Is A Very Neat Ids'
to_title '   ': '   '
to_title '  a   c  ': '  A   C  '
remove_prefix 'ananab'/'an' : ab
remove_prefix 'anatnab'/'an': atnab
remove_suffix 'banana'/'na' : ba
remove_suffix 'bantana'/'na': banta

find_str/rfind_str (input string 'abcdefghi')
-----------------------------------------------------
find_str: 0
find_str: -1
find_str: -1
find_str: 4
find_str: 4
find_str: -1
find_str: 0
find_str: -1
find_str: -1
find_str: 4
find_str: 4
find_str: -1