What type of testing cannot be performed on scheduled flows?

Scheduled flows are designed to execute automatically at specified times, which limits the scope of certain testing types. Visual testing involves verifying the user interface elements and how they appear when users interact with the system. Since scheduled flows typically run in the background without a user interface, there is no visual aspect to test. Therefore, visual testing cannot be performed on scheduled flows, making this the correct choice.

The other types of testing are more suited to scheduled flows. Integration testing focuses on checking how various system components work together, which can be accomplished by observing the scheduled flow's interactions with other systems and data sources. Functional testing verifies that the flow operates as intended by examining its functionality in various scenarios, which can also be executed despite the flow's scheduled nature. Unit testing involves testing individual components of the flow in isolation, confirming that each part performs correctly on its own; this can be conducted regardless of the flow being scheduled.

Thus, the inability to conduct visual testing aligns well with the characteristics of scheduled flows.