= ANSI::Diff

  require 'ansi/diff'

  a = 'abcYefg'
  b = 'abcXefg'

  diff = ANSI::Diff.new(a,b)

  diff.to_s.assert == "\e[31mabc\e[0m\e[33mYefg\e[0m\n\e[31mabc\e[0mXefg"

Try another.

  a = 'abc'
  b = 'abcdef'

  diff = ANSI::Diff.new(a,b)

  diff.to_s.assert == "\e[31mabc\e[0m\n\e[31mabc\e[0mdef"

And another.

  a = 'abcXXXghi'
  b = 'abcdefghi'

  diff = ANSI::Diff.new(a,b)

  diff.to_s.assert == "\e[31mabc\e[0m\e[33mXXXghi\e[0m\n\e[31mabc\e[0mdefghi"

And another.

  a = 'abcXXXdefghi'
  b = 'abcdefghi'

  diff = ANSI::Diff.new(a,b)

  diff.to_s.assert == "\e[31mabc\e[0m\e[33mXXX\e[0m\e[35mdefghi\e[0m\n\e[31mabc\e[0m\e[35mdefghi\e[0m"

Comparison that is mostly different.

  a = 'abcpppz123'
  b = 'abcxyzzz43'

  diff = ANSI::Diff.new(a,b)

  diff.to_s.assert == "\e[31mabc\e[0m\e[33mpppz123\e[0m\n\e[31mabc\e[0mxyzzz43"

