Method subcase_start

test/doctest.h:5612–5618

        }

        void subcase_start(const SubcaseSignature& in) override {
            xml.startElement("SubCase")
                    .writeAttribute("name", in.m_name)
                    .writeAttribute("filename", skipPathFromFilename(in.m_file))
                    .writeAttribute("line", line(in.m_line));
            xml.ensureTagClosed();
        }

        void subcase_end() override { xml.endElement(); }