Function replace_once

tests/test_support/readme.py:103–106

Replace ``old`` with ``new`` in ``text``, asserting exactly one occurrence.

(text: str, old: str, new: str)

def replace_once(text: str, old: str, new: str) -> str:
    """Replace ``old`` with ``new`` in ``text``, asserting exactly one occurrence."""
    assert text.count(old) == 1, f"Expected exactly one occurrence of {old!r}"
    return text.replace(old, new)


def run_bash_blocks(