Changes to server state can be handled by setting a new
vignettes, these are handled by creating subdirectories with integer names.
This function increments that integer subdirectory and adds it to
.mockPaths() so that changed server state can be captured and loaded.
Invisibly, the return of
.mockPaths() with the new path added.
In a vignette,
put a call to
change_state() before any code block that makes a change on
the server, or rather, before any code block that might repeat the same
request previously done and expect a different result.