Dedent Common Whitespace From Multiline String

I'm adding tests to cover some custom logic in the usage messages that are produced by Click in a CLI I'm building. The usage output is a mutliline string formatted with some indentation. On top of that, I'm putting it in a Python test file with some additional syntactical indentation.

If this was Ruby, I would reach for the <<~ heredoc syntax. The closest equivalent to that in Python is textwrap.dedent.

Remove any common leading whitespace from every line in text.

This can be used to make triple-quoted strings line up with the left edge of the display, while still presenting them in the source code in indented form.

import textwrap

def test_base_help_message():
    runner = BetterCliRunner()

    help_result = runner.invoke(cli, ["--help"])
    output = textwrap.dedent("""\
        Usage: vmt [OPTIONS] COMMAND [ARGS]...

        Options:
          -v, --verbose  See extra output when running commands
          --help         Show this message and exit.

        Commands:
          cancel
          log
          start
          status
          stop
    """)
    assert output in help_result.output

Before adding in textwrap.dedent, the test was failing because of bits of extra whitespace that wasn't matching up with the actual CLI output.

Note: the leading \ after the opening """ is needed to remove the leading newline that would otherwise be included.