ses = db.getMongo().startSession()
    dbs = ses.getDatabase("test")

    printjson(dbs.createCollection("c", {writeConcern: {w: "majority"}}))

    print("TRANSACTION 1")
    printjson(ses.startTransaction())
    printjson(dbs.c.insert({_id: 0}))
    printjson(ses.commitTransaction())

    print("TRANSACTION 2")
    printjson(ses.startTransaction())
    printjson(dbs.c.insert({_id: 1}))
    printjson(ses.commitTransaction())

assert: command failed: {
	"operationTime" : Timestamp(1524048246, 2),
	"ok" : 0,
	"errmsg" : "WriteConflict",
	"code" : 112,
	"codeName" : "WriteConflict",
	"$clusterTime" : {
		"clusterTime" : Timestamp(1524048246, 3),
		"signature" : {
			"hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
			"keyId" : NumberLong(0)
		}
	}
}