Speed up functional tests with ops_test.fast_forward() (#65)

ops_test.fast_forward() temporarily speeds up the update-status firing
rate. This is effectively equal to setting and resetting the
"update-status-hook-interval" model config before and after the relevant
code.

Previously, we would have had to spend 5m waiting for the unit
status change to be detected after any state change to the
hardware-exporter systemd service.

Refer: https://github.com/charmed-kubernetes/pytest-operator/blob/main/docs/reference.md#async-def-fast_forwardself-fast_interval-str--10s-slow_interval-optionalstr--none

tests/functional/test_charm.py

@@ -162,34 +162,38 @@ async def test_10_start_and_stop_exporter(self, app, unit, sync_helper, ops_test
         """Test starting and stopping the exporter results in correct charm status."""
         # Stop the exporter
         stop_cmd = "systemctl stop hardware-exporter"
-        await asyncio.gather(
-            unit.run(stop_cmd),
-            ops_test.model.wait_for_idle(apps=[APP_NAME], status="blocked", timeout=TIMEOUT),
-        )
-        assert unit.workload_status_message == AppStatus.NOT_RUNNING
+        async with ops_test.fast_forward():
+            await asyncio.gather(
+                unit.run(stop_cmd),
+                ops_test.model.wait_for_idle(apps=[APP_NAME], status="blocked", timeout=TIMEOUT),
+            )
+            assert unit.workload_status_message == AppStatus.NOT_RUNNING
 
         # Start the exporter
         start_cmd = "systemctl start hardware-exporter"
-        await asyncio.gather(
-            unit.run(start_cmd),
-            ops_test.model.wait_for_idle(apps=[APP_NAME], status="active", timeout=TIMEOUT),
-        )
-        assert unit.workload_status_message == AppStatus.READY
+        async with ops_test.fast_forward():
+            await asyncio.gather(
+                unit.run(start_cmd),
+                ops_test.model.wait_for_idle(apps=[APP_NAME], status="active", timeout=TIMEOUT),
+            )
+            assert unit.workload_status_message == AppStatus.READY
 
     async def test_11_exporter_failed(self, app, unit, sync_helper, ops_test):
         """Test failure in the exporter results in correct charm status."""
         # Setting incorrect log level will crash the exporter
-        await asyncio.gather(
-            app.set_config({"exporter-log-level": "RANDOM_LEVEL"}),
-            ops_test.model.wait_for_idle(apps=[APP_NAME], status="blocked", timeout=TIMEOUT),
-        )
-        assert unit.workload_status_message == AppStatus.UNHEALTHY
+        async with ops_test.fast_forward():
+            await asyncio.gather(
+                app.set_config({"exporter-log-level": "RANDOM_LEVEL"}),
+                ops_test.model.wait_for_idle(apps=[APP_NAME], status="blocked", timeout=TIMEOUT),
+            )
+            assert unit.workload_status_message == AppStatus.UNHEALTHY
 
-        await asyncio.gather(
-            app.reset_config(["exporter-log-level"]),
-            ops_test.model.wait_for_idle(apps=[APP_NAME], status="active", timeout=TIMEOUT),
-        )
-        assert unit.workload_status_message == AppStatus.READY
+        async with ops_test.fast_forward():
+            await asyncio.gather(
+                app.reset_config(["exporter-log-level"]),
+                ops_test.model.wait_for_idle(apps=[APP_NAME], status="active", timeout=TIMEOUT),
+            )
+            assert unit.workload_status_message == AppStatus.READY
 
     async def test_20_on_remove_event(self, app, sync_helper, ops_test):
         """Test _on_remove event cleans up the service on the host machine."""