override default hosts

src/client/options/mod.rs

@@ -1205,7 +1205,11 @@ impl ClientOptions {
     /// Applies the options in other to these options if a value is not already present
     #[cfg(test)]
     pub(crate) fn merge(&mut self, other: ClientOptions) {
-        if self.hosts.is_empty() {
+        let default_hosts = vec![ServerAddress::Tcp {
+            host: "localhost".to_string(),
+            port: Some(27017),
+        }];
+        if self.hosts.is_empty() || self.hosts == default_hosts {
             self.hosts = other.hosts;
         }
         merge_options!(