Fix effect cleanup

src/index.tsx

@@ -191,12 +191,21 @@ export function useEffectReducer<
     >,
     event: TEvent | FlushEvent
   ): AggregatedEffectsState<TState, TEvent> => {
+    // Remove stopped entities if any, but otherwise keep them around
+    // if they haven't been stopped yet since this means our cleanup
+    // useEffect hasn't been executed yet
+    entitiesToStop = entitiesToStop.some(
+      entity => entity.status === EntityStatus.Stopped
+    )
+      ? entitiesToStop.filter(entity => entity.status !== EntityStatus.Stopped)
+      : entitiesToStop;
+
     const nextEffectEntities: Array<EffectEntity<TState, TEvent>> = [];
     const nextEntitiesToStop: Array<EffectEntity<TState, TEvent>> = [];
 
     if (event.type === flushEffectsSymbol) {
       // Record that effects have already been executed
-      return [state, stateEffectTuples.slice(event.count), nextEntitiesToStop];
+      return [state, stateEffectTuples.slice(event.count), entitiesToStop];
     }
 
     const exec = (

test/useEffectReducer.test.tsx

@@ -507,10 +507,14 @@ describe('useEffectReducer', () => {
     const helloButton = getByTestId('send-hello');
     const goodbyeButton = getByTestId('send-goodbye');
 
+    // Click each button twice to make sure no effect cleanup
+    // is skipped due to batching
+    fireEvent.click(helloButton);
     fireEvent.click(helloButton);
 
     setTimeout(() => {
       fireEvent.click(goodbyeButton);
+      fireEvent.click(goodbyeButton);
     }, 30);
 
     await waitFor(() => {