How to use the black.read_cache function in black

def test_cache_broken_file(self) -> None:
        mode = black.FileMode()
        with cache_dir() as workspace:
            cache_file = black.get_cache_file(mode)
            with cache_file.open("w") as fobj:
                fobj.write("this is not a pickle")
            self.assertEqual(black.read_cache(mode), {})
            src = (workspace / "test.py").resolve()
            with src.open("w") as fobj:
                fobj.write("print('hello')")
            self.invokeBlack([str(src)])
            cache = black.read_cache(mode)
            self.assertIn(src, cache)

def test_single_file_force_pyi(self) -> None:
        reg_mode = black.FileMode()
        pyi_mode = black.FileMode(is_pyi=True)
        contents, expected = read_data("force_pyi")
        with cache_dir() as workspace:
            path = (workspace / "file.py").resolve()
            with open(path, "w") as fh:
                fh.write(contents)
            self.invokeBlack([str(path), "--pyi"])
            with open(path, "r") as fh:
                actual = fh.read()
            # verify cache with --pyi is separate
            pyi_cache = black.read_cache(pyi_mode)
            self.assertIn(path, pyi_cache)
            normal_cache = black.read_cache(reg_mode)
            self.assertNotIn(path, normal_cache)
        self.assertEqual(actual, expected)

source, expected = read_data("force_py36")
        with cache_dir() as workspace:
            paths = [
                (workspace / "file1.py").resolve(),
                (workspace / "file2.py").resolve(),
            ]
            for path in paths:
                with open(path, "w") as fh:
                    fh.write(source)
            self.invokeBlack([str(p) for p in paths] + PY36_ARGS)
            for path in paths:
                with open(path, "r") as fh:
                    actual = fh.read()
                self.assertEqual(actual, expected)
            # verify cache with --target-version is separate
            pyi_cache = black.read_cache(py36_mode)
            normal_cache = black.read_cache(reg_mode)
            for path in paths:
                self.assertIn(path, pyi_cache)
                self.assertNotIn(path, normal_cache)

def test_failed_formatting_does_not_get_cached(self) -> None:
        mode = black.FileMode()
        with cache_dir() as workspace, patch(
            "black.ProcessPoolExecutor", new=ThreadPoolExecutor
        ):
            failing = (workspace / "failing.py").resolve()
            with failing.open("w") as fobj:
                fobj.write("not actually python")
            clean = (workspace / "clean.py").resolve()
            with clean.open("w") as fobj:
                fobj.write('print("hello")\n')
            self.invokeBlack([str(workspace)], exit_code=123)
            cache = black.read_cache(mode)
            self.assertNotIn(failing, cache)
            self.assertIn(clean, cache)

def test_read_cache_line_lengths(self) -> None:
        mode = black.FileMode()
        short_mode = black.FileMode(line_length=1)
        with cache_dir() as workspace:
            path = (workspace / "file.py").resolve()
            path.touch()
            black.write_cache({}, [path], mode)
            one = black.read_cache(mode)
            self.assertIn(path, one)
            two = black.read_cache(short_mode)
            self.assertNotIn(path, two)

def test_read_cache_line_lengths(self) -> None:
        mode = black.FileMode()
        short_mode = black.FileMode(line_length=1)
        with cache_dir() as workspace:
            path = (workspace / "file.py").resolve()
            path.touch()
            black.write_cache({}, [path], mode)
            one = black.read_cache(mode)
            self.assertIn(path, one)
            two = black.read_cache(short_mode)
            self.assertNotIn(path, two)

def test_write_cache_read_cache(self) -> None:
        mode = black.FileMode()
        with cache_dir() as workspace:
            src = (workspace / "test.py").resolve()
            src.touch()
            black.write_cache({}, [src], mode)
            cache = black.read_cache(mode)
            self.assertIn(src, cache)
            self.assertEqual(cache[src], black.get_cache_info(src))

src: Path,
    line_length: int,
    write_back: black.WriteBack,
    mode: black.FileMode,
    clear_output: bool,
    report: black.Report,
) -> None:
    """Reformat a single file under `src`."""
    try:

        sub_report = SubReport(write_back=write_back)
        changed = black.Changed.NO

        cache: black.Cache = {}
        if write_back is not black.WriteBack.DIFF:
            cache = black.read_cache(line_length, mode)
            res_src = src.resolve()
            if res_src in cache and cache[res_src] == black.get_cache_info(
                res_src
            ):
                changed = black.Changed.CACHED
        if changed is not black.Changed.CACHED:
            sub_report = format_file_in_place(
                src,
                line_length=line_length,
                write_back=write_back,
                mode=mode,
                clear_output=clear_output,
                sub_report=sub_report,
            )
            if sub_report.change_count:
                changed = black.Changed.YES