As of January 1st, 2016 most of the tax advantages of a testamentary trust have ended. However there are still a few useful things a testamentary trust can do.
Testamentary trusts can only be created by a direction in a Will. These types of trusts allowed estate assets to flow into them and allowed the option for income generated by the assets taxed within the trust at a graduated rate. So beneficiaries at a higher tax rate could withdraw income from the trust which could be taxed at a lower rate.
As of January 1st, income not paid out to beneficiaries is taxed at the higher rate which exceeds 50%. There are still situations which make testamentary trusts useful as an estate planning tool. For example, assets left to children can be directed to a trust managed by a trustee named in the Will who can provide guidance for the children until the age when the deceased directed the assets be handed over to the children. A trust managed by a responsible trustee can also prevent a spendthrift beneficiary from wasting the assets.
So if you have directed your assets be held in a trust for your children, this may still be a good thing. The graduated tax rates for testamentary trusts can still be used for up to 3 years after death. However, if there are no tax advantages or risk of mismanagement of the funds, a testamentary trust may create a layer of complexity not needed. Testamentary trusts do have tax filing requirements. I recommend you have your Wills reviewed if you do have a trust clause and determine if any changes are recommended.