diff --git a/cylc/flow/tests/network/test_schema.py b/cylc/flow/tests/network/test_schema.py
new file mode 100644
index 00000000000..34d483654ee
--- /dev/null
+++ b/cylc/flow/tests/network/test_schema.py
@@ -0,0 +1,35 @@
+# THIS FILE IS PART OF THE CYLC SUITE ENGINE.
+# Copyright (C) 2008-2019 NIWA & British Crown (Met Office) & Contributors.
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+"""Tests for cylc.flow.network.schema"""
+
+import asyncio
+from types import AsyncGeneratorType
+
+from cylc.flow.network.schema import to_subscription
+
+
+def test_to_subscription():
+    """Test to_subscription function."""
+    async def async_callable():
+        return []
+
+    assert asyncio.iscoroutine(async_callable())
+
+    async_generator = to_subscription(async_callable)
+
+    assert not asyncio.iscoroutine(async_generator())
+    assert isinstance(async_generator(), AsyncGeneratorType)