As reported in #4807, if we have a test assertion failure, we get \n printed as characters instead of actual newlines, making stacktraces and error messages ugly to read.
r3974 was the commit to introduced cxxtest. It was version 3.10.1 (2004-12-01), see https://trac.wildfiregames.com/browser/ps/trunk/libraries/cxxtest/Versions?rev=3974
cxxtest's TS_FAIL method requires a const char *message.
That is true since its introduction (see https://trac.wildfiregames.com/browser/ps/trunk/libraries/cxxtest/include/cxxtest/TestSuite.h?rev=3974#L41)
and for the most recent version 4.4 added in r15667 (see https://trac.wildfiregames.com/browser/ps/trunk/libraries/source/cxxtest-4.4/cxxtest/TestSuite.h#L58).
r7259 introduced script_TS_FAIL(void*, std::wstring msg) calling TS_FAIL(msg). The missing conversion from std::wstring to char* results in the mentioned newline error and can be fixed by just adding the conversion.