Add test for the Selector class

Signed-off-by: Leandro Lucarella <[email protected]>

Author: llucax

tests/utils/test_selector.py

@@ -0,0 +1,55 @@
+# License: MIT
+# Copyright © 2023 Frequenz Energy-as-a-Service GmbH
+
+"""Tests for the Selector implementation."""
+
+from unittest import mock
+
+import pytest
+
+from frequenz.channels import Receiver, ReceiverStoppedError
+from frequenz.channels.util import Selected, selected_from
+
+
+class TestSelected:
+    """Tests for the Selected class."""
+
+    def test_with_value(self) -> None:
+        """Test selected from a receiver with a value."""
+        recv = mock.MagicMock(spec=Receiver[int])
+        recv.consume.return_value = 42
+        selected = Selected[int](recv)
+
+        assert selected_from(selected, recv)
+        assert selected.value == 42
+        assert selected.exception is None
+        assert not selected.was_stopped()
+
+    def test_with_exception(self) -> None:
+        """Test selected from a receiver with an exception."""
+        recv = mock.MagicMock(spec=Receiver[int])
+        exception = Exception("test")
+        recv.consume.side_effect = exception
+        selected = Selected[int](recv)
+
+        assert selected_from(selected, recv)
+        with pytest.raises(Exception, match="test"):
+            _ = selected.value
+        assert selected.exception is exception
+        assert not selected.was_stopped()
+
+    def test_with_stopped(self) -> None:
+        """Test selected from a stopped receiver."""
+        recv = mock.MagicMock(spec=Receiver[int])
+        exception = ReceiverStoppedError[int](recv)
+        recv.consume.side_effect = exception
+        selected = Selected[int](recv)
+
+        assert selected_from(selected, recv)
+        with pytest.raises(
+            ReceiverStoppedError,
+            match=r"Receiver <MagicMock spec='_GenericAlias' id='\d+'> was stopped",
+        ):
+            _ = selected.value
+        assert selected.exception is exception
+        assert selected.was_stopped()