> use test
switched to db test
> db.test.usuarios.insert({"nombre":"Nicolas","email":"nicolas@nothotmail.com"})
WriteResult({ "nInserted" : 1 })
> show collections
system.indexes
test.usuarios
> db.test.usuarios.createIndex({email:1},{unique:true})
{
	"createdCollectionAutomatically" : false,
	"numIndexesBefore" : 1,
	"numIndexesAfter" : 2,
	"ok" : 1
}
> db.test.usuarios.insert({"nombre":"JuanPePe","email":"nicolas@nothotmail.com"})
WriteResult({
	"nInserted" : 0,
	"writeError" : {
		"code" : 11000,
		"errmsg" : "insertDocument :: caused by :: 11000 E11000 duplicate key error index: test.test.usuarios.$email_1  dup key: { : \"nicolas@nothotmail.com\" }"
	}
})
> db.test.usuarios.insert({"nombre":"JuanPePe","email":"juanpep@suemail.com"})
WriteResult({ "nInserted" : 1 })
> db.test.usuarios.find()
{ "_id" : ObjectId("550e910df49799b8c6496cb8"), "nombre" : "Nicolas", "email" : "nicolas@nothotmail.com" }
{ "_id" : ObjectId("550e91a9f49799b8c6496cbc"), "nombre" : "JuanPePe", "email" : "juanpep@suemail.com" }