What makes you think that the first attack was some sort of a "test"?
Because I just watched the entire 3rd season and it was referred to as "just a probe" numerous times.
Here is one of the transcripts from the first episode of the 3rd season "The Xindi"
[Xindi Council Chamber]
HUMANOID: It could simply be a coincidence.
REPTILIAN: You're being naive. Their planet is fifty light years away. It is not a coincidence.
HUMANOID: How do you know your contacts gave you accurate information?
INSECTOID: It's the beginning of an invasion. Hundreds of Earth ships will follow.
HUMANOID: They have no way of knowing that we launched the probe.
INSECTOID: We must destroy the vessel.
REPTILIAN: How many humans are aboard?
INSECTOID: It doesn't matter. They must be destroyed before they find the weapon.
ARBOREAL: When will it be ready?
DEGRA: The next series of tests is being prepared.
REPTILIAN: You will accomplish nothing if all you do is run tests.
ARBOREAL: We must be patient. We must follow the plan that we all agreed to.
AQUATIC: Our future is at stake. This council mustn't be divided.
HUMANOID: (to Reptilian) Learn everything you can about this human vessel.
First they refer to "the probe" and later they refer to the actual "weapon."