Add the local npc_parts.py head/face/hand part pipeline with tests and docs

tools/tests/test_npc_parts.py

@@ -0,0 +1,51 @@
+import contextlib
+import io
+import tempfile
+import unittest
+from pathlib import Path
+
+import npc_parts
+
+
+class CliTests(unittest.TestCase):
+    def test_part_names_are_known(self):
+        self.assertEqual(
+            set(npc_parts.PART_NAMES),
+            {"head", "face", "hand_l", "hand_r"},
+        )
+
+    def test_blender_commands_fail_cleanly_without_bpy(self):
+        # Outside Blender, build/extract/assemble/inspect must explain the
+        # flatpak invocation instead of raising.
+        for cmd in ("build", "extract", "assemble", "inspect"):
+            with self.subTest(cmd=cmd):
+                code = npc_parts._needs_blender(cmd)
+                self.assertEqual(code, 2)
+
+    def test_sheet_rejects_missing_directory(self):
+        with self.assertRaises(SystemExit) as ctx:
+            npc_parts.make_sheet("/nonexistent/does-not-exist", "/tmp/x.jpg")
+        self.assertIn("not a directory", str(ctx.exception))
+
+    def test_compare_rejects_missing_directory(self):
+        with self.assertRaises(SystemExit) as ctx:
+            npc_parts.compare("/nonexistent", "/nonexistent2", "/tmp/x.jpg")
+        self.assertIn("not a directory", str(ctx.exception))
+
+
+class SheetTests(unittest.TestCase):
+    def test_sheet_builds_from_real_pngs(self):
+        with tempfile.TemporaryDirectory() as td:
+            td = Path(td)
+            Image, _ = npc_parts._pillow()
+            for i in range(3):
+                im = Image.new("RGB", (64, 64), (i * 60, 0, 0))
+                im.save(td / f"f{i}.png")
+            out = td / "sheet.jpg"
+            result = npc_parts.make_sheet(str(td), str(out))
+            self.assertEqual(Path(result).suffix, ".jpg")
+            self.assertTrue(out.is_file())
+
+
+if __name__ == "__main__":
+    unittest.main()