Bug 154757

In CPP unit tests, that use cppunit [1], there are helpful assertion macros with _MESSAGE, like CPPUNIT_ASSERT_MESSAGE. These take a string as the first argument, which is output when the test fails, providing additional context, often useful in loops.

See e.g. testTdf154319 in sw/qa/extras/ooxmlimport/ooxmlimport2.cxx, which constructs the message, showing which property in which level is being tested, so that the failure provides enough context.

However, it's impossible to use our string types (and their familiar operations, like concatenations and number conversions) as the message. The use of OString requires passing C-style pointer from getStr call; OUString requires conversion to UTF-8-encoded OString first; and concatenations need to be explicitly converted to OString, too, like in testTdf112118_DOCX (sw/qa/extras/ooxmlexport/ooxmlexport11.cxx).

cppunit uses overloads of CPPUNIT_NS::message_to_string to convert the message argument to std::string.

The task is to provide appropriate conversion overloads for OString and OUString, and then simplify the places in tests that currently do the conversions themselves. The suggested place where these overloads could be placed is include/o3tl/cppunittraitshelper.hxx.

The result should, for example, convert the current code in testTdf112118_DOCX from

>            CPPUNIT_ASSERT_EQUAL_MESSAGE(OString(sStage + " margin width").getStr(),
>                side.nMargin, nMargin);


into

>            CPPUNIT_ASSERT_EQUAL_MESSAGE(sStage + " margin width",
>                side.nMargin, nMargin);


[1] https://git.libreoffice.org/cppunit