Use same data for test and validation
You use your validation_set to tune your model. It means that you don`t train on this data but the model takes it into account. For example, you use it to tune the model's hyperparameters. 
In order to have a good evaluation - as test set you should use a data which is totally unknown to this model.
Hey I am training a CNN model , and was wondering what will happen if I use the same data for validation and test?
Does the model train on validation data as well? (Does my model see the validation data?) Or just the error and accuracy are calculatd and taken into account for training?