Add some missing replay code (#56)

beavers/replay.py

@@ -1,4 +1,5 @@
 """Module for replaying historical data."""
+
 import abc
 import collections.abc
 import dataclasses
@@ -36,6 +37,11 @@ class ReplayContext:
     end: pd.Timestamp
     frequency: pd.Timedelta
 
+    def __post_init__(self):
+        """Check arguments are valid."""
+        assert self.start.tzname() == "UTC"
+        assert self.end.tzname() == "UTC"
+
 
 class DataSource(Protocol[T]):
     """Interface for replaying historical data from a file or database."""
@@ -363,3 +369,20 @@ def _next(self) -> Optional[DataSource]:
             return next(self._sources)
         except StopIteration:
             return None
+
+
+class NoOpDataSink(DataSink):
+    """DataSink that does nothing."""
+
+    def append(self, timestamp: pd.Timestamp, data: T):
+        pass
+
+    def close(self):
+        pass
+
+
+class NoOpDataSinkProvider:
+    """DataSinkProvider that provides a NoOpDataSink."""
+
+    def __call__(self, context: ReplayContext) -> DataSink[T]:
+        return NoOpDataSink()

tests/test_replay.py

@@ -8,6 +8,7 @@
 from beavers.replay import (
     DataSource,
     IteratorDataSourceAdapter,
+    NoOpDataSinkProvider,
     ReplayContext,
     ReplayDriver,
     T,
@@ -316,3 +317,10 @@ def test_replay_run_cycle():
     assert metrics.warp_ratio > 0.0
     assert driver.current_time == pd.to_datetime("2023-01-02 12:00:00Z")
     assert driver.is_done()
+
+
+def test_no_op():
+    provider = NoOpDataSinkProvider()
+    data_sink = provider(ReplayContext(UTC_MAX, UTC_MAX, pd.to_timedelta("1s")))
+    data_sink.append(UTC_MAX, None)
+    data_sink.close()