Add basic validation of noto for android file

.gitignore

@@ -1 +1,2 @@
 venv/
+__pycache__/

tests/noto_fonts_for_android_test.py

@@ -1,4 +1,57 @@
+from lxml import etree
+from pathlib import Path
 import pytest
 
-def test_noto_for_android_paths():
-  pass
+
+_KNOWN_PATHLESS = {
+  "NotoSansSyriacEastern-Regular.ttf",
+  "NotoSansSyriacWestern-Regular.ttf",
+  "NotoSansSymbols-Regular-Subsetted.ttf",
+  "NotoColorEmoji.ttf",
+  "NotoColorEmojiFlags.ttf",
+  "NotoSansSymbols-Regular-Subsetted2.ttf",
+  "NotoSansSoyombo-VF.ttf",
+}
+
+
+def _repo_root() -> Path:
+  root = (Path(__file__).parent / "..").absolute()
+  if not (root / "LICENSE").is_file():
+    raise IOError(f"{root} does not contain LICENSE")
+  return root
+
+
+def _noto_4_android_file() -> Path:
+  xml_file = _repo_root() / "android-connection" / "noto-fonts-4-android.xml"
+  if not xml_file.is_file():
+    raise IOError(f"No file {xml_file}")
+  return xml_file
+
+
+def _font_file(font_el) -> str:
+  return ("".join(font_el.itertext())).strip()
+
+
+def test_fonts_have_path():
+  root = etree.parse(str(_noto_4_android_file()))
+  bad = []
+  for font in root.iter("font"):
+    font_file = _font_file(font)
+    if font_file in _KNOWN_PATHLESS:
+      assert "path" not in font.attrib, f"{font_file} not expected to have path. Correct _KNOWN_PATHLESS if you just added path"
+      continue
+
+    if not font.attrib.get("path", ""):
+      bad.append(font_file)
+  assert not bad, "Missing path attribute: " + ", ".join(bad)
+
+
+def test_font_paths_are_valid():
+  root = etree.parse(str(_noto_4_android_file()))
+  bad = []
+  for font in root.xpath("//font[@path]"):
+    path = font.attrib["path"]
+    file = _font_file(font)
+    if not (_repo_root() / path / file).is_file():
+      bad.append((path, file))
+  assert not bad, "No such file: " + ", ".join(bad)