A testamentary trust, unlike other trusts, is not legally binding until the person has died. As such, a person must include the trust in their will so that it is created upon death.
When you draft a will, it is a good idea to include the creation of a testamentary trust. Probate will still take place. This is to make sure the assets are being managed appropriately.
It is easier to include the testamentary trust clause that creates the trust when you are creating a will – however, if you already have a will, you can always amend the will to include the testamentary trust clause.