A test set is the data set used to:

a. estimate performance of candidate models on unseen data.

b. estimate performance of the final model on unseen data.

c. build the data mining model.

d. show counts of actual versus predicted class values.

C.

Step-by-step explanation:

The "training" data set is the general term for the samples used to create the model, while the "test" or "validation" data set is used to qualify performance. Perhaps traditionally the dataset used to evaluate the final model performance is called the "test set".