Complex sentence: Functional testing is done basically a test of user interactions with may be external systems.As gray-box testing can efficiently suits for functional testing due to its characteristics; it also helps to confirm that software meets the requirements defined for the software.
Split into simpler sentences: Functional testing is done basically a test of user interactions with may be external systems. Gray-box testing is well-suited for functional testing due to its characteristics; it also helps to confirm that software meets the requirements defined for the software.