Pin to a single host in GridFS tests (#500)

Author: Divjot Arora

mongo/gridfs/gridfs_test.go

@@ -35,8 +35,16 @@ func TestGridFS(t *testing.T) {
 			}
 		},
 	}
-	clientOpts := options.Client().ApplyURI(cs.Original).SetReadPreference(readpref.Primary()).
-		SetWriteConcern(writeconcern.New(writeconcern.WMajority())).SetPoolMonitor(poolMonitor)
+	clientOpts := options.Client().
+		ApplyURI(cs.Original).
+		SetReadPreference(readpref.Primary()).
+		SetWriteConcern(writeconcern.New(writeconcern.WMajority())).
+		SetPoolMonitor(poolMonitor).
+		// Connect to a single host. For sharded clusters, this will pin to a single mongos, which avoids
+		// non-deterministic versioning errors in the server. This has no effect for replica sets because the driver
+		// will discover the other hosts during SDAM checks.
+		SetHosts(cs.Hosts[:1])
+
 	client, err := mongo.Connect(context.Background(), clientOpts)
 	assert.Nil(t, err, "Connect error: %v", err)
 	db := client.Database("gridfs")