update formatting and add spec test

Author: saghm

src/sdam/description/topology/mod.rs

@@ -209,7 +209,7 @@ impl TopologyDescription {
     /// Check the cluster for a compatibility error, and record the error message if one is found.
     fn check_compatibility(&mut self) {
         self.compatibility_error = None;
-        
+
         for server in self.servers.values() {
             let error_message = server.compatibility_error_message();
 

src/test/spec/json/server-discovery-and-monitoring/single/too_old_then_upgraded.json

@@ -0,0 +1,54 @@
+{
+  "description": "Standalone with default maxWireVersion of 0 is upgraded to one with maxWireVersion 6",
+  "uri": "mongodb://a",
+  "phases": [
+    {
+      "responses": [
+        [
+          "a:27017",
+          {
+            "ok": 1,
+            "ismaster": true
+          }
+        ]
+      ],
+      "outcome": {
+        "servers": {
+          "a:27017": {
+            "type": "Standalone",
+            "setName": null
+          }
+        },
+        "topologyType": "Single",
+        "logicalSessionTimeoutMinutes": null,
+        "setName": null,
+        "compatible": false
+      }
+    },
+    {
+      "responses": [
+        [
+          "a:27017",
+          {
+            "ok": 1,
+            "ismaster": true,
+            "minWireVersion": 0,
+            "maxWireVersion": 6
+          }
+        ]
+      ],
+      "outcome": {
+        "servers": {
+          "a:27017": {
+            "type": "Standalone",
+            "setName": null
+          }
+        },
+        "topologyType": "Single",
+        "logicalSessionTimeoutMinutes": null,
+        "setName": null,
+        "compatible": true
+      }
+    }
+  ]
+}

src/test/spec/json/server-discovery-and-monitoring/single/too_old_then_upgraded.yml

@@ -0,0 +1,46 @@
+description: "Standalone with default maxWireVersion of 0 is upgraded to one with maxWireVersion 6"
+uri: "mongodb://a"
+phases: [
+    {
+        responses: [
+                ["a:27017", {
+                    ok: 1,
+                    ismaster: true
+                }]
+        ],
+        outcome: {
+            servers: {
+                "a:27017": {
+                    type: "Standalone",
+                    setName:
+                }
+            },
+            topologyType: "Single",
+            logicalSessionTimeoutMinutes: null,
+            setName: ,
+            compatible: false
+        }
+    },
+    {
+        responses: [
+                ["a:27017", {
+                    ok: 1,
+                    ismaster: true,
+                    minWireVersion: 0,
+                    maxWireVersion: 6
+                }]
+        ],
+        outcome: {
+            servers: {
+                "a:27017": {
+                    type: "Standalone",
+                    setName:
+                }
+            },
+            topologyType: "Single",
+            logicalSessionTimeoutMinutes: null,
+            setName: ,
+            compatible: true
+        }
+    }
+]