In generate-expected-outputs read the test definition with utf8 encoding.

test/subset/generate-expected-outputs.py

@@ -3,6 +3,7 @@
 # Pre-generates the expected output subset files (via fonttools) for
 # specified subset test suite(s).
 
+import io
 import os
 import sys
 
@@ -26,7 +27,7 @@ if not args:
 	usage()
 
 for path in args:
-	with open(path, 'r') as f:
+	with io.open(path, mode="r", encoding="utf-8") as f:
 		test_suite = SubsetTestSuite(path, f.read())
 		output_directory = test_suite.get_output_directory()