Handle variable fonts like cascadia code that dont have a postfix variation prefix name for some of their faces

kitty_tests/fonts.py

@@ -8,10 +8,18 @@ import unittest
 from functools import partial
 
 from kitty.constants import is_macos, read_kitty_resource
-from kitty.fast_data_types import DECAWM, get_fallback_font, sprite_map_set_layout, sprite_map_set_limits, test_render_line, test_sprite_position_for, wcwidth
+from kitty.fast_data_types import (
+    DECAWM,
+    get_fallback_font,
+    sprite_map_set_layout,
+    sprite_map_set_limits,
+    test_render_line,
+    test_sprite_position_for,
+    wcwidth,
+)
 from kitty.fonts import family_name_to_key
 from kitty.fonts.box_drawing import box_chars
-from kitty.fonts.common import all_fonts_map, face_from_descriptor, get_font_files, get_named_style
+from kitty.fonts.common import FontSpec, all_fonts_map, face_from_descriptor, get_font_files, get_named_style, spec_for_face
 from kitty.fonts.render import coalesce_symbol_maps, render_string, setup_for_testing, shape_string
 from kitty.options.types import Options
 from kitty.options.utils import parse_font_spec
@@ -93,6 +101,18 @@ class Selection(BaseTest):
             d = get_font_files(opts)['medium']
             face = face_from_descriptor(d)
             self.ae(get_named_style(face)['name'], 'Black')
+        if has('cascadia code'):
+            opts = Options()
+            opts.font_family = parse_font_spec('family="cascadia code"')
+            opts.italic_font = parse_font_spec('family="cascadia code" variable_name= style="Light Italic"')
+            ff = get_font_files(opts)
+
+            def t(x, **kw):
+                kw['family'] = 'Cascadia Code'
+                face = face_from_descriptor(ff[x])
+                self.ae(FontSpec(**kw).as_setting, spec_for_face('Cascadia Code', face).as_setting)
+            t('medium', variable_name='CascadiaCodeRoman', style='Regular')
+            t('italic', variable_name='', style='Light Italic')
 
 
 class Rendering(BaseTest):