Test improvements - Filename and text context

[Flamefire]

To better determine the position of a failed test print the filename in the error message and add support for context-messages:

The first is useful for tests in commonly used headers, the latter in loops over different test inputs

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.81%. Comparing base (69e0e30) to head (f0d95b0).
Report is 3 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #244   +/-   ##
========================================
  Coverage    95.81%   95.81%           
========================================
  Files          117      117           
  Lines        10352    10352           
========================================
  Hits          9919     9919           
  Misses         433      433           

Files with missing lines	Coverage Δ
test/test_catalog.cpp	100.00% <100.00%> (ø)
test/test_codecvt.cpp	100.00% <100.00%> (ø)
test/test_date_time.cpp	100.00% <ø> (ø)
test/test_encoding.cpp	100.00% <100.00%> (ø)
test/test_formatting.cpp	100.00% <100.00%> (ø)

---

Continue to review full report in Codecov by Sentry.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 69e0e30...f0d95b0. Read the comment docs.