ttCollection_test: check loading TTCollection with lazy attribute

currently lazy=True fails with 'ValueError: seek of closed file'

Tests/ttLib/ttCollection_test.py

@@ -0,0 +1,14 @@
+import os
+from fontTools.ttLib import TTCollection
+import pytest
+
+TTX_DATA_DIR = os.path.join(os.path.dirname(__file__), "..", "ttx", "data")
+
+
+@pytest.mark.parametrize("lazy", [None, True, False])
+def test_lazy_open(lazy):
+    ttc = os.path.join(TTX_DATA_DIR, "TestTTC.ttc")
+    with TTCollection(ttc, lazy=lazy) as collection:
+        assert len(collection) == 2
+        assert collection[0]["maxp"].numGlyphs == 6
+        assert collection[1]["maxp"].numGlyphs == 6