From 2969ba5d05ccb9e7218ecf6ddf56df66c2a68f20 Mon Sep 17 00:00:00 2001
From: Niko Kivel <niko.kivel@lightsource.ca>
Date: Thu, 9 Jan 2025 14:57:23 +0000
Subject: [PATCH] assert removed from StandardReadable.add_readables - added
 TypeGaurd to make Pylance happy. - added TypeError raised test

---
 src/ophyd_async/core/_readable.py | 40 ++++++++++++++++++-------------
 tests/core/test_readable.py       | 19 +++++++++++++++
 2 files changed, 43 insertions(+), 16 deletions(-)

diff --git a/src/ophyd_async/core/_readable.py b/src/ophyd_async/core/_readable.py
index 4c424d7d9a..3215dcd8d9 100644
--- a/src/ophyd_async/core/_readable.py
+++ b/src/ophyd_async/core/_readable.py
@@ -2,7 +2,7 @@
 from collections.abc import Awaitable, Callable, Generator, Sequence
 from contextlib import contextmanager
 from enum import Enum
-from typing import Any, cast
+from typing import Any, TypeGuard, cast
 
 from bluesky.protocols import HasHints, Hints, Reading
 from event_model import DataKey
@@ -205,6 +205,14 @@ def add_readables(
             `StandardReadableFormat` documentation
         """
 
+        def is_signalr(device: Device) -> TypeGuard[SignalR]:
+            return isinstance(device, SignalR)
+
+        def assert_device_is_signalr(device: Device) -> SignalR:
+            if not is_signalr(device):
+                raise TypeError(f"{device} is not a SignalR")
+            return device
+
         for device in devices:
             match format:
                 case StandardReadableFormat.CHILD:
@@ -219,24 +227,24 @@ def add_readables(
                     if isinstance(device, HasHints):
                         self._has_hints += (device,)
                 case StandardReadableFormat.CONFIG_SIGNAL:
-                    assert isinstance(device, SignalR), f"{device} is not a SignalR"
-                    self._describe_config_funcs += (device.describe,)
-                    self._read_config_funcs += (device.read,)
+                    signalr_device = assert_device_is_signalr(device=device)
+                    self._describe_config_funcs += (signalr_device.describe,)
+                    self._read_config_funcs += (signalr_device.read,)
                 case StandardReadableFormat.HINTED_SIGNAL:
-                    assert isinstance(device, SignalR), f"{device} is not a SignalR"
-                    self._describe_funcs += (device.describe,)
-                    self._read_funcs += (device.read,)
-                    self._stageables += (device,)
-                    self._has_hints += (_HintsFromName(device),)
+                    signalr_device = assert_device_is_signalr(device=device)
+                    self._describe_funcs += (signalr_device.describe,)
+                    self._read_funcs += (signalr_device.read,)
+                    self._stageables += (signalr_device,)
+                    self._has_hints += (_HintsFromName(signalr_device),)
                 case StandardReadableFormat.UNCACHED_SIGNAL:
-                    assert isinstance(device, SignalR), f"{device} is not a SignalR"
-                    self._describe_funcs += (device.describe,)
-                    self._read_funcs += (_UncachedRead(device),)
+                    signalr_device = assert_device_is_signalr(device=device)
+                    self._describe_funcs += (signalr_device.describe,)
+                    self._read_funcs += (_UncachedRead(signalr_device),)
                 case StandardReadableFormat.HINTED_UNCACHED_SIGNAL:
-                    assert isinstance(device, SignalR), f"{device} is not a SignalR"
-                    self._describe_funcs += (device.describe,)
-                    self._read_funcs += (_UncachedRead(device),)
-                    self._has_hints += (_HintsFromName(device),)
+                    signalr_device = assert_device_is_signalr(device=device)
+                    self._describe_funcs += (signalr_device.describe,)
+                    self._read_funcs += (_UncachedRead(signalr_device),)
+                    self._has_hints += (_HintsFromName(signalr_device),)
 
 
 class _UncachedRead:
diff --git a/tests/core/test_readable.py b/tests/core/test_readable.py
index 8ab69ed03c..7d2771bd66 100644
--- a/tests/core/test_readable.py
+++ b/tests/core/test_readable.py
@@ -209,6 +209,25 @@ def test_standard_readable_add_readables_adds_to_expected_attrs(
     assert_sr_has_attrs(sr, expected_attrs)
 
 
+@pytest.mark.parametrize(
+    "format",
+    [
+        Format.CONFIG_SIGNAL,
+        Format.HINTED_SIGNAL,
+        Format.UNCACHED_SIGNAL,
+        Format.HINTED_UNCACHED_SIGNAL,
+    ],
+)
+def test_standard_readable_add_readables_raises_signalr_typeerror(format) -> None:
+    # Mock a Device instance that is not a SignalR
+    mock_device = MagicMock(spec=Device)
+    sr = StandardReadable()
+
+    # Ensure it raises TypeError
+    with pytest.raises(TypeError, match=f"{mock_device} is not a SignalR"):
+        sr.add_readables([mock_device], format=format)
+
+
 def test_standard_readable_config_signal():
     signal_r = MagicMock(spec=SignalR)
     sr = StandardReadable()