add mongos

Author: Thomas Reggi

lib/core/sdam/topology_description.js

@@ -151,8 +151,19 @@ class TopologyDescription {
     // update the actual server description
     serverDescriptions.set(address, serverDescription);
 
+    if (serverType === ServerType.Mongos) {
+      return new TopologyDescription(
+        TopologyType.Sharded,
+        serverDescriptions,
+        setName,
+        maxSetVersion,
+        maxElectionId,
+        commonWireVersion,
+        this.options
+      );
+    }
+
     if (topologyType === TopologyType.Single) {
-      // once we are defined as single, that never changes
       return new TopologyDescription(
         TopologyType.Single,
         serverDescriptions,