Fix start equal end in ring buffer window

Restore the typical list-like behavior for equal start and end. Would be
inconsistent with the forbidden case start > end.

Signed-off-by: cwasicki <[email protected]>

Author: cwasicki

src/frequenz/sdk/timeseries/_ringbuffer/buffer.py

@@ -292,6 +292,9 @@ def window(
                 f"end parameter {end} has to predate start parameter {start}"
             )
 
+        if start == end:
+            return np.array([]) if isinstance(self._buffer, np.ndarray) else []
+
         start_index = self.datetime_to_index(start)
         end_index = self.datetime_to_index(end)
 

tests/timeseries/test_ringbuffer.py

@@ -522,6 +522,13 @@ def test_window() -> None:
     assert [0, 1, 2] == list(win)
     win = buffer.window(dt(0), dt(3), force_copy=False)
     assert [0, 1, 2] == list(win)
+    # Empty array
+    assert 0 == buffer.window(dt(1), dt(1)).size
+
+    buffer = get_orb([0.0, 1.0, 2.0, 3.0, 4.0])  # type: ignore
+    assert [0, 1, 2] == buffer.window(dt(0), dt(3))
+    assert [] == buffer.window(dt(0), dt(0))
+    assert [] == buffer.window(dt(1), dt(1))
 
 
 def test_wrapped_buffer_window() -> None: