The water from inside the test tube most likely came from the blue copper sulfate crystal which is a hydrated salt.
Hydrated salts contain water of hydration.
A blue copper sulfate crystal contains water of hydration.
When heated, the water evaporates off to give an anhydrous salt which appears colorless.
The equation of the reaction is as follows:
CuSO4•5H2O -----> CuSO4 + 5H2O(g)
More on water of hydration can be found here: https://brainly.com/question/919417