How to use the uharfbuzz.Buffer function in uharfbuzz

def test_cluster_level(self):
        buf = hb.Buffer()

        assert buf.cluster_level == hb.BufferClusterLevel.DEFAULT

        buf.cluster_level = hb.BufferClusterLevel.MONOTONE_CHARACTERS
        assert buf.cluster_level == hb.BufferClusterLevel.MONOTONE_CHARACTERS

        buf.cluster_level = hb.BufferClusterLevel.MONOTONE_GRAPHEMES
        assert buf.cluster_level == hb.BufferClusterLevel.MONOTONE_GRAPHEMES

        buf.cluster_level = hb.BufferClusterLevel.CHARACTERS
        assert buf.cluster_level == hb.BufferClusterLevel.CHARACTERS

        buf.cluster_level = hb.BufferClusterLevel.DEFAULT
        assert buf.cluster_level == hb.BufferClusterLevel.DEFAULT

def test_glyh_name_no_features(self, blankfont, string, expected):
        buf = hb.Buffer()
        buf.add_str(string)
        buf.guess_segment_properties()
        hb.shape(blankfont, buf)
        # font.get_glyph_name() returns None if the font does not contain glyph names
        # or if the glyph ID does not exist.
        glyph_names = [blankfont.get_glyph_name(g.codepoint) for g in buf.glyph_infos]
        assert glyph_names == expected
        assert blankfont.get_glyph_name(1000) is None
        # font.glyph_to_string() return "gidN" if the font does not contain glyph names
        # or if the glyph ID does not exist.
        glyph_names = [blankfont.glyph_to_string(g.codepoint) for g in buf.glyph_infos]
        assert glyph_names == expected
        assert blankfont.glyph_to_string(1000) == 'gid1000'

def test_gid_and_cluster_no_features(self, blankfont, string, expected):
        buf = hb.Buffer()
        buf.add_str(string)
        buf.guess_segment_properties()
        hb.shape(blankfont, buf)
        infos = [(g.codepoint, g.cluster) for g in buf.glyph_infos]
        assert infos == expected

def test_add_utf8(self):
        buf = hb.Buffer()
        buf.add_utf8("aбç💩e".encode("utf-8"))
        infos = [(g.codepoint, g.cluster) for g in buf.glyph_infos]
        assert infos == [(0x61, 0), (0x431, 1), (0xE7, 3), (0x1F4A9, 5), (0x65, 9)]

def test_message_func_crash(self, blankfont):
        string = "edcba"
        buf = hb.Buffer()
        buf.add_str(string)
        buf.guess_segment_properties()
        message_collector = MessageCollector()
        buf.set_message_func(message_collector.message)
        hb.shape(blankfont, buf)

def shapeHB(text, font_name, font_size, features: Dict[str, bool] = None):
    font = pdfmetrics.getFont(font_name)
    if not isinstance(font, TTFont):
        # TODO make valid for all types of fonts
        raise RLKerningError("Not a TTF font")

    fontdata = font.face._ttf_data
    face = hb.Face(fontdata)
    font = hb.Font(face)

    # HB scales to integers in offset and advance so very big scale
    # will divide by SCALE_MULT to get the actual size in fractional points
    font.scale = (font_size * SCALE_MULT, font_size * SCALE_MULT)
    hb.ot_font_set_funcs(font)
    buf = hb.Buffer()
    buf.add_str(text)
    buf.guess_segment_properties()
    hb.shape(font, buf, features)

    return buf