*Exception.Show used to work differently when the traceback contains one frame
vs more frames. Harmonize how they work, and consistent with how parse errors
and compilation errors are shown.
- Use reflection to derive function name.
- Take test cases as variadic arguments, instead of requiring them to be wrapped
in a Table.
- Support naming test cases.
- Run test cases as subtests with t.Run.
Qualified imports of pkg/tt outnumber unqualified (27 to 24). Improve
consistency, and clarity, by changing the dot (unqualified) imports of
that package symbols to qualified.
This change is a preparation step for refining all *Op types to return Exception
as the error.
Keeping Exception as a struct type will make such a change error-prone, since
a (*Exception)(nil) != error(nil), so if an *Op returns a nil *Exception, it
is not nil if the return value is stored in an error-typed variable.
* Use a "type" field to identify the type, instead of predicates in the exc:
module.
* Make the reason values behave more like structmaps, including a Repr that
mimics a map.
This fixes#208.
