Researchers randomly assign study participants to one of two groups: the participants receiving the artificial sweetener are in the group and the individuals receiving the sugar packets are in the group.

test, control

Explanation:

In an experiment, there will be always a group of individuals, that are going to simulate the normal conditions, in this case the people that are receiving the sugar packets are the one that is called control.  This group are simulating the natural diet, the one that it has been used since humankind discover the sugar cane.

The other group, the one that is receiving the artificial sweetener is called the test group because is the "new" substance that is going to be compare with the ancient, traditional sugar.

In a research, when you have to groups like this, you can compare the effect of the new substance like if the insulin level increases or decreases or still the same.