Every test had the same pattern of a main catching exceptions and
returning 0 or 1 based on that. Factor that into test.hpp.
As most code in test.hpp is only executed on failure and those should
not occur this file is excluded from coverage.
Finally test.hpp is included last and the header to test first
consistently to check for self-sufficient includes.
Make some functions protected to derive a test class from stackstring
which can be used to detect wether a stack or heap value is used
Fix or silence issues from static analyser findings
Double-check and handle surrogates in iostream
