fix: remove possibility of zero-effect Stop from api watcher test

This handles a situation where we may be entrant into the eventCh case in
the call to Next when Stop is called. In that case, the default clause
will be invoked and we effectively ignore the stop call. This means the
watcher will never stop, causing test failure.

api/watcher/watcher_test.go

@@ -100,26 +100,31 @@ func setupWatcher[T any](c *gc.C, caller *apimocks.MockAPICaller, facadeName str
 	eventCh := make(chan T)
 
 	stopped := make(chan bool)
-	caller.EXPECT().APICall(gomock.Any(), facadeName, 666, "id-666", "Stop", nil, gomock.Any()).DoAndReturn(func(_ context.Context, _ string, _ int, _ string, _ string, _ any, _ any) error {
-		select {
-		case stopped <- true:
-		default:
-		}
-		return nil
-	}).Return(nil).AnyTimes()
-
-	caller.EXPECT().APICall(gomock.Any(), facadeName, 666, "id-666", "Next", nil, gomock.Any()).DoAndReturn(func(_ context.Context, _ string, _ int, _ string, _ string, _ any, r any) error {
-		select {
-		case ev, ok := <-eventCh:
-			if !ok {
-				c.FailNow()
+	caller.EXPECT().APICall(gomock.Any(), facadeName, 666, "id-666", "Stop", nil, gomock.Any()).DoAndReturn(
+		func(context.Context, string, int, string, string, any, any) error {
+			select {
+			case stopped <- true:
+			case <-time.After(testing.LongWait):
+				c.Fatalf("timed out waiting for stop call")
 			}
-			*(*r.(*any)).(*any) = ev
 			return nil
-		case <-stopped:
-		}
-		return &params.Error{Code: params.CodeStopped}
-	}).AnyTimes()
+		},
+	).Return(nil).AnyTimes()
+
+	caller.EXPECT().APICall(gomock.Any(), facadeName, 666, "id-666", "Next", nil, gomock.Any()).DoAndReturn(
+		func(_ context.Context, _ string, _ int, _ string, _ string, _ any, r any) error {
+			select {
+			case ev, ok := <-eventCh:
+				if !ok {
+					c.Fatalf("next channel closed")
+				}
+				*(*r.(*any)).(*any) = ev
+				return nil
+			case <-stopped:
+			}
+			return &params.Error{Code: params.CodeStopped}
+		},
+	).AnyTimes()
 	return "id-666", eventCh
 }