Make sure there are no collection name conflicts in createCollection test.

Author: matthewdale

source/causal-consistency/tests/causal-consistency-write-commands.json

@@ -1001,12 +1001,20 @@
             }
           ]
         },
+        {
+          "name": "dropCollection",
+          "object": "database0",
+          "arguments": {
+            "session": "session0",
+            "collection": "causal-consistency-createCollection-test"
+          }
+        },
         {
           "name": "createCollection",
           "object": "database0",
           "arguments": {
             "session": "session0",
-            "collection": "newcoll"
+            "collection": "causal-consistency-createCollection-test"
           }
         }
       ],
@@ -1028,11 +1036,22 @@
                 }
               }
             },
+            {
+              "commandStartedEvent": {
+                "commandName": "drop",
+                "command": {
+                  "drop": "causal-consistency-createCollection-test",
+                  "lsid": {
+                    "$$sessionLsid": "session0"
+                  }
+                }
+              }
+            },
             {
               "commandStartedEvent": {
                 "commandName": "create",
                 "command": {
-                  "create": "newcoll",
+                  "create": "causal-consistency-createCollection-test",
                   "lsid": {
                     "$$sessionLsid": "session0"
                   },

source/causal-consistency/tests/causal-consistency-write-commands.yml

@@ -336,15 +336,27 @@ tests:
   - description: "create includes afterClusterTime in causally consistent session"
     operations:
       - *find
+      # Drop the collection first to make sure there's no name conflict during
+      # createCollection.
+      - name: dropCollection
+        object: *database0
+        arguments:
+          session: *session0
+          collection: &newCollectionName causal-consistency-createCollection-test
       - name: createCollection
         object: *database0
         arguments:
           session: *session0
-          collection: &newCollectionName newcoll
+          collection: *newCollectionName
     expectEvents:
       - client: *client0
         events:
           - *findEvent
+          - commandStartedEvent:
+              commandName: drop
+              command:
+                drop: *newCollectionName
+                lsid: { $$sessionLsid: *session0 }
           - commandStartedEvent:
               commandName: create
               command: