group function Null safety
- Object description,
 - void body(
 - {dynamic skip}
 
Creates a group of tests.
A group's description (converted to a string) is included in the descriptions of any tests or sub-groups it contains. setUp and tearDown are also scoped to the containing group.
If skip is a String or true, the group is skipped. If it's a String, it
should explain why the group is skipped; this reason will be printed instead
of running the group's tests.
Implementation
@isTestGroup
void group(Object description, void Function() body, { dynamic skip }) {
  _declarer.group(description.toString(), body, skip: skip);
}