Current version in Fedora Rawhide is NUnit 2.6.4 There is currently NUnit 3.4.1 available at https://github.com/nunit/nunit/releases/tag/3.4.1 This is also required for MonoDevelop 6.0 Problem is that the NUnit gui has been split from NUnit 3.x, and the current state is not stable yet. see https://github.com/nunit/nunit-gui So we cannot just replace NUnit 2.x with NUnit 3.x plus a new nunit-gui package yet. The suggestion from Claudio was to add a package nunit2 for compatibility. https://bugzilla.redhat.com/show_bug.cgi?id=1313236#c4
I have done some preparation work: https://github.com/tpokorra/lbs-mono-fedora/tree/master/nunit upgraded to NUnit 3.4.1 and https://github.com/tpokorra/lbs-mono-fedora/tree/master/nunit2 provides the legacy NUnit2 and nunit2-gui package I will put that into rawhide when it proves to work in the copr (https://copr.fedorainfracloud.org/coprs/tpokorra/mono/) first