The wheat and the weeds parable is not written so one might fear if they're really genuine, a wheat or a weed (tare). This misses the point entirely. The weeds are sown by Satan, they know they are weeds, and God knows, and the angels will know. If you are not a believer in Christ, you know that you don't believe, you know that you are a weed. Likewise if you believe, you know you're genuine, you know you're wheat. Assurance is of the essence of salvation. The point is not to ask whether one is a wheat or weed, the point is to recognize that there are wheat and weeds and so in Christ's kingdom there will be genuine and fake and the conflicts that this causes. Because the world will know we are Christians by our love for one another, one point of evidence is that if someone doesn't seem to love a brother or sister, then you may question whether they are a wheat or a weed.