void tearDown(dynamic callback())

Registers a function to be run after tests.

This function will be called after each test is run. callback may be asynchronous; if so, it must return a Future.

If this is called within a test group, it applies only to tests in that group. callback will be run before any tear-down callbacks in parent groups or at the top level.

Each callback at the top level or in a given group will be run in the reverse of the order they were declared.

Source 

void tearDown(callback()) => _declarer.tearDown(callback);