Let's say we have a team consisting of a developer and a tester. And we have a Kanban board consisting of "Development(WIP=1)", "Testing(WIP=1)", "Done" columns.
When the developer has implemented a task he moves it to the "Testing" column.
Everything is OK so far.
But tester can also write new tests. Should he put this task in "Development" column?
If yes, then the tester can be working on two tasks at the same time despite the WIP = 1 (one task in "Development" column and one task in "Testing" column).
If no, then a Kanban board represents the division of a team into developers, testers etc, but not a team's workflow.