rate-limiting: Redis keys have wrong TTL when sync_rate > 0 #14995

  describe("redis with sync rate > 0 and key missing in redis at sync time", function()
    local EXPIRATION = require "kong.plugins.rate-limiting.expiration"

    local redis
    local conf = {
      route_id = uuid(),
      service_id = uuid(),
      redis_host = helpers.redis_host,
      redis_port = helpers.redis_port,
      redis_database = 0,
      sync_rate = 1,
    }

    before_each(function()
      local red = require "resty.redis"
      redis = assert(red:new())
      redis:set_timeout(1000)
      assert(redis:connect(conf.redis_host, conf.redis_port))
      redis:flushall()
    end)

    after_each(function()
      redis:close()
    end)

    for _, period in ipairs { "minute", "hour" } do
      it("sets a TTL no longer than one " .. period .. " when recreating the key", function()
        local identifier = uuid()
        -- same unit the handler uses (milliseconds)
        local current_timestamp = ngx.time() * 1000
        local periods = timestamp.get_timestamps(current_timestamp)
        local cache_key = get_local_key(conf, identifier, period, periods[period])

        -- populates the local cache, including the key's expire_at
        assert(policies.redis.usage(conf, identifier, period, current_timestamp))

        -- simulate the key expiring in redis before the pending delta is synced
        assert(redis:del(cache_key))

        assert(policies.redis.increment(conf, { [period] = 10 }, identifier, current_timestamp, 1))
        assert(policies.redis.increment(conf, { [period] = 10 }, identifier, current_timestamp, 1))

        -- give time to the async sync to recreate the key
        ngx.sleep(1 + conf.sync_rate)

        local ttl = assert(redis:ttl(cache_key))
        assert(ttl > 0 and ttl <= EXPIRATION[period],
          "expected TTL in (0, " .. EXPIRATION[period] .. "], got " .. ttl)
      end)
    end
  end)