add unit tests for verifying

tests/test_request_cancel.py

@@ -0,0 +1,34 @@
+import pytest
+import asyncio
+import contextlib
+
+from sanic.response import text
+
+
+async def test_request_cancel_when_connection_lost(loop, app, test_client):
+    app.still_serving_cancelled_request = False
+
+    @app.get('/')
+    async def handler(request):
+        await asyncio.sleep(1.0)
+        # at this point client is already disconnected
+        app.still_serving_cancelled_request = True
+        return text('OK')
+
+    test_cli = await test_client(app)
+
+    # schedule client call
+    task = loop.create_task(test_cli.get('/'))
+    loop.call_later(0.01, task)
+    await asyncio.sleep(0.5)
+
+    # cancelling request and closing connection after 0.5 sec
+    task.cancel()
+
+    with contextlib.suppress(asyncio.CancelledError):
+        await task
+
+    # Wait for server and check if it's still serving the cancelled request
+    await asyncio.sleep(1.0)
+
+    assert app.still_serving_cancelled_request is False