1、修改mongo_collection:createIndex的bug

2、增加mongo_collection:drop和mongo_collection:dropIndex（方便测试代码清理环境）
3、根据自己项目用到的功能，增加了测试代码

test/testmongodb.lua

@@ -0,0 +1,90 @@
+local skynet = require "skynet"
+local mongo = require "mongo"
+local bson = require "bson"
+
+local host, db_name = ...
+
+function test_insert_without_index()
+	local db = mongo.client({host = host})
+
+	db[db_name].testdb:dropIndex("*")
+	db[db_name].testdb:drop()
+
+	local ret = db[db_name].testdb:safe_insert({test_key = 1});
+	assert(ret and ret.n == 1)
+
+	local ret = db[db_name].testdb:safe_insert({test_key = 1});
+	assert(ret and ret.n == 1)
+end
+
+function test_insert_with_index()
+	local db = mongo.client({host = host})
+
+	db[db_name].testdb:dropIndex("*")
+	db[db_name].testdb:drop()
+
+	db[db_name].testdb:ensureIndex({test_key = 1}, {unique = true, name = "test_key_index"})
+
+	local ret = db[db_name].testdb:safe_insert({test_key = 1})
+	assert(ret and ret.n == 1)
+
+	local ret = db[db_name].testdb:safe_insert({test_key = 1})
+	assert(ret and ret.n == 0)
+end
+
+function test_find_and_remove()
+	local db = mongo.client({host = host})
+
+	db[db_name].testdb:dropIndex("*")
+	db[db_name].testdb:drop()
+
+	db[db_name].testdb:ensureIndex({test_key = 1}, {unique = true, name = "test_key_index"})
+
+	local ret = db[db_name].testdb:safe_insert({test_key = 1})
+	assert(ret and ret.n == 1)
+
+	local ret = db[db_name].testdb:findOne({test_key = 1})
+	assert(ret and ret.test_key == 1)
+
+	db[db_name].testdb:delete({test_key = 1})
+
+	local ret = db[db_name].testdb:findOne({test_key = 1})
+	assert(ret == nil)
+end
+
+
+function test_expire_index()
+	local db = mongo.client({host = host})
+
+	db[db_name].testdb:dropIndex("*")
+	db[db_name].testdb:drop()
+
+	db[db_name].testdb:ensureIndex({test_key = 1}, {unique = true, name = "test_key_index", expireAfterSeconds = 1, })
+	db[db_name].testdb:ensureIndex({test_date = 1}, {expireAfterSeconds = 1, })
+
+	local ret = db[db_name].testdb:safe_insert({test_key = 1, test_date = bson.date(os.time())})
+	assert(ret and ret.n == 1)
+
+	local ret = db[db_name].testdb:findOne({test_key = 1})
+	assert(ret and ret.test_key == 1)
+
+	for i = 1, 1000 do
+		skynet.sleep(11);
+		
+		local ret = db[db_name].testdb:findOne({test_key = 1})
+		if ret == nil then
+			return
+		end
+	end
+
+	assert(false, "test expire index failed");
+end
+
+skynet.start(function()
+	test_insert_without_index()
+	test_insert_with_index()
+	test_find_and_remove()
+	test_expire_index()
+
+	print("mongodb test finish.");
+end)