How to use the black.format_file_contents function in black

def test_format_file_contents(self) -> None:
        empty = ""
        mode = black.FileMode()
        with self.assertRaises(black.NothingChanged):
            black.format_file_contents(empty, mode=mode, fast=False)
        just_nl = "\n"
        with self.assertRaises(black.NothingChanged):
            black.format_file_contents(just_nl, mode=mode, fast=False)
        same = "j = [1, 2, 3]\n"
        with self.assertRaises(black.NothingChanged):
            black.format_file_contents(same, mode=mode, fast=False)
        different = "j = [1,2,3]"
        expected = same
        actual = black.format_file_contents(different, mode=mode, fast=False)
        self.assertEqual(expected, actual)
        invalid = "return if you can"
        with self.assertRaises(black.InvalidInput) as e:
            black.format_file_contents(invalid, mode=mode, fast=False)
        self.assertEqual(str(e.exception), "Cannot parse: 1:7: return if you can")

def normalize_formatting(code: str) -> str:
    """Returns a string of the code with normalized formatting for easier compares"""
    try:
        return black.format_file_contents(code, line_length=88, fast=True)
    except black.NothingChanged:
        return code

def test_format_file_contents(self) -> None:
        empty = ""
        mode = black.FileMode()
        with self.assertRaises(black.NothingChanged):
            black.format_file_contents(empty, mode=mode, fast=False)
        just_nl = "\n"
        with self.assertRaises(black.NothingChanged):
            black.format_file_contents(just_nl, mode=mode, fast=False)
        same = "j = [1, 2, 3]\n"
        with self.assertRaises(black.NothingChanged):
            black.format_file_contents(same, mode=mode, fast=False)
        different = "j = [1,2,3]"
        expected = same
        actual = black.format_file_contents(different, mode=mode, fast=False)
        self.assertEqual(expected, actual)
        invalid = "return if you can"
        with self.assertRaises(black.InvalidInput) as e:
            black.format_file_contents(invalid, mode=mode, fast=False)
        self.assertEqual(str(e.exception), "Cannot parse: 1:7: return if you can")

def format_text(*, text, config):
    mode = black.FileMode(
        target_versions=config["target_version"],
        line_length=config["line_length"],
        is_pyi=config["pyi"],
        string_normalization=not config["skip_string_normalization"],
    )

    return black.format_file_contents(text, fast=config["fast"], mode=mode)

else:
                with open(self.filename, "rb") as buf:
                    source, _, _ = black.decode_bytes(buf.read())
        except Exception as e:
            source = ""
            msg = "900 Failed to load file: %s" % e

        if not source and not msg:
            # Empty file (good)
            return
        elif source:
            # Call black...
            try:
                file_mode = self._file_mode
                file_mode.is_pyi = self.filename and self.filename.endswith(".pyi")
                new_code = black.format_file_contents(
                    source, mode=file_mode, fast=False
                )
            except black.NothingChanged:
                return
            except black.InvalidInput:
                msg = "901 Invalid input."
            except BadBlackConfig as err:
                msg = "997 Invalid TOML file: %s" % err
            except Exception as err:
                msg = "999 Unexpected exception: %s" % err
            else:
                assert (
                    new_code != source
                ), "Black made changes without raising NothingChanged"
                line, col = find_diff_start(source, new_code)
                line += 1  # Strange as col seems to be zero based?