Add specific test for when data was not fetched

archon/actor/delegate.py

@@ -352,6 +352,10 @@ async def readout(
         except Exception as err:
             return self.fail(f"Failed reading out: {err}")
 
+        if len(c_fdata) == 0:
+            self.command.error("No data was fetched.")
+            return False
+
         self.command.debug(f"Readout completed in {time()-t0:.1f} seconds.")
 
         if write is False:
@@ -391,8 +395,7 @@ async def readout(
             for fd in fdata
         ]
 
-        if len(fdata) > 0:
-            self.last_exposure_no = fdata[0]["exposure_no"]
+        self.last_exposure_no = fdata[0]["exposure_no"]
 
         # Prepare checksum information.
         write_checksum: bool = self.config["checksum.write"]

tests/actor/test_delegate.py

@@ -264,6 +264,25 @@ async def test_delegate_shutter_fails(delegate: ExposureDelegate, mocker):
     assert result is False
 
 
+async def test_delegate_readout_no_fetch_data(delegate: ExposureDelegate):
+    command = Command("", actor=delegate.actor)
+    result = await delegate.expose(
+        command,
+        [delegate.actor.controllers["sp1"]],
+        flavour="object",
+        exposure_time=0.01,
+        readout=False,
+    )
+    assert result is True
+
+    assert delegate.expose_data
+    delegate.expose_data.controllers = []
+
+    result = await delegate.readout(command)
+    assert result is False
+    assert delegate.command.replies[-1].body["error"] == "No data was fetched."
+
+
 @pytest.mark.parametrize("window_mode", ["test_mode", "default"])
 async def test_delegate_expose_window_mode(delegate: ExposureDelegate, window_mode):
     command = Command("", actor=delegate.actor)