How to use the flynt.api._fstringify_file function in flynt

def test_works(formattable_file):

    with open(formattable_file) as f:
        content_before = f.read()

    modified, _, _, _ = _fstringify_file(formattable_file, True, 1000)

    with open(formattable_file) as f:
        content_after = f.read()

    assert modified
    assert content_after != content_before

def test_catches_subtle(formattable_file, monkeypatch):

    with open(formattable_file) as f:
        content_before = f.read()

    def broken_fstringify_by_line(*args, **kwargs):
        return "a = 42", 42

    monkeypatch.setattr(api, "fstringify_code_by_line", broken_fstringify_by_line)

    modified, _, _, _ = _fstringify_file(formattable_file, True, 1000)

    with open(formattable_file) as f:
        content_after = f.read()

    assert not modified
    assert content_after == content_before

def test_break_safe(formattable_file, monkeypatch):

    with open(formattable_file) as f:
        content_before = f.read()

    def broken_fstringify_by_line(*args, **kwargs):
        return "Hello World", 42

    monkeypatch.setattr(api, "fstringify_code_by_line", broken_fstringify_by_line)

    modified, _, _, _ = _fstringify_file(formattable_file, True, 1000)

    with open(formattable_file) as f:
        content_after = f.read()

    assert not modified
    assert content_after == content_before

def try_on_file_string_concat(filename: str, multiline):
    """ Given a file name (something.py) find this file in test/integration/samples_in,
    run flint_str on its content, write result
    to test/integration/actual_out/something.py,
    and compare the result with test/integration/expected_out/something.py"""
    txt_in = read_in(filename)
    path = write_output_file(filename, txt_in)

    _fstringify_file(path, multiline=multiline, len_limit=120, transform_concat=True)
    out = read_output_file(filename)

    return out, read_expected(filename)

def test_py2(py2_file):

    with open(py2_file) as f:
        content_before = f.read()

    modified, _, _, _ = _fstringify_file(py2_file, True, 1000)

    with open(py2_file) as f:
        content_after = f.read()

    assert not modified
    assert content_after == content_before