In Agile, particularly in Scrum, testing-related activities should ideally be integrated into the development process from the beginning of the Sprint. Therefore, "Option 3: Right from the beginning of the Sprint" is the most appropriate choice.

Testing activities, such as test planning, test design, and test execution, should be performed in parallel with coding and other development activities. This helps identify and address issues early in the Sprint and ensures that potentially shippable increments of the product can be delivered at the end of each Sprint.