mongodb/jstests/mmap_v1/index_check1.js

db.somecollection.drop();

assert.eq(0, db.system.namespaces.find({name: /somecollection/}).length(), "1");

db.somecollection.save({a: 1});

assert.eq(2, db.system.namespaces.find({name: /somecollection/}).length(), "2");

db.somecollection.ensureIndex({a: 1});

var z = db.system.namespaces.find({name: /somecollection/}).length();
assert.gte(z, 1, "3");

if (z == 1)
    print("warning: z==1, should only happen with alternate storage engines");

db.somecollection.drop();

assert.eq(0, db.system.namespaces.find({name: /somecollection/}).length(), "4");

db.somecollection.save({a: 1});

assert.eq(2, db.system.namespaces.find({name: /somecollection/}).length(), "5");

db.somecollection.ensureIndex({a: 1});

var x = db.system.namespaces.find({name: /somecollection/}).length();
assert(x == 2 || x == z, "6");

assert(db.somecollection.validate().valid, "7");