test: add issue reference

Author: HemangChothani

test/test_suite.py

@@ -1374,16 +1374,27 @@ class IsOrIsNotDistinctFromTest(_IsOrIsNotDistinctFromTest):
 
 
 class OrderByLabelTest(_OrderByLabelTest):
-    @pytest.mark.skip("Spanner doesn't supports composed GROUP BY.")
+    @pytest.mark.skip(
+        "Spanner requires an alias for the GROUP BY list when specifying derived "
+        "columns also used in SELECT"
+    )
     def test_group_by_composed(self):
         pass
 
 
 class CompoundSelectTest(_CompoundSelectTest):
-    @pytest.mark.skip("Spanner throws a syntax error.")
+    """
+    See: https://github.com/googleapis/python-spanner/issues/347
+    """
+
+    @pytest.mark.skip(
+        "Spanner DBAPI incorrectly classify the statement starting with brackets."
+    )
     def test_limit_offset_selectable_in_unions(self):
         pass
 
-    @pytest.mark.skip("Spanner throws a syntax error.")
+    @pytest.mark.skip(
+        "Spanner DBAPI incorrectly classify the statement starting with brackets."
+    )
     def test_order_by_selectable_in_unions(self):
         pass