The issue is described here: https://github.com/bjorn/tiled/pull/1545
Quoting that page:
That is, I can see that it's not linking to Qt5QuickTestd.lib, but I don't know what the submodule name for that is. I tried "quicktest", but no cigar. http://doc.qt.io/qbs/qt-modules.html#list-of-submodules doesn't mention anything.
I did a quick grep and found this file, which doesn't seem to contain any Qt Quick test stuff.
"qmltest" appears to be the correct module name, but is not listed on http://doc.qt.io/qbs/qt-modules.html.