claration of ```std::ostream``` and that is what the library does - but it is forbidden by the standard. It currently works everywhere - on all tested compilers - but if the user wishes to be 100% standards compliant - then the [**```DOCTEST_CONFIG_USE_STD_HEADERS```**](configuration.html#doctest_config_use_std_headers) identifier can be used to force the inclusion of ```<iosfwd>```. The reason the header is not included by default is that on MSVC (for example) it drags a whole bunch of stuff with it - and 