void configureRouterNavigator(
FnxRouterNavigator navigator
)

This method allows you to inject custom implementation of FnxRouterNavigator, we use it in tests, there is probably no good reason for doing it.

Source

/// This method allows you to inject custom implementation of FnxRouterNavigator,
/// we use it in tests, there is probably no good reason for doing it.
void configureRouterNavigator(FnxRouterNavigator navigator) {
  _navigator = navigator;
}