Add QDebug::toString()

Often I want to construct a useful message for test failures by including a textual representation of an object involved with the failure. Creating such a message is easy when using QDebug, because I can just use my existing operator<< for that object's type, but the QTest framework requires a string. This results in code like the following:

    if (!list.isEmpty()) {
        QString message;
        QDebug debug(&message);
        debug << "Expected list to be empty, but it still contains the following items:" << list;
        QFAIL(qPrintable(message));
    }

This is even worse for checks that must be repeated over time, as there is no simple way to do the above test without the QTRY_* macros.

What I recently did was define a toString() template function that simply stores the result of calling operator<< with the object and returns it:

    template <typename T>
    QString toString(const T &object) {
        QString buffer;
        QDebug stream(&buffer);
        stream << object;
        return buffer;
    }

It can then be used like this:

QTRY_VERIFY2(list.isEmpty(), qPrintable(QString::fromLatin1(
        "Expected list to be empty, but it still contains the following items: %1").arg(QtUtils::toString(list))));

I think that this would be a really convenient addition for debug output in tests, and possibly other places where strings are required.

QTest already has a toString API that is only used for printing types in failures in its macros, otherwise that could have also been a good place to add the proposed function.