As a long time debian/devuan user I always feel ashamed to ask such a
pedestrian question as this.

Given the absence of a backport for nano, my aim is to construct
a .deb for the testing version of nano (nano-9.5). This is what I did:

In apt sources.list IO added the lines

    deb http://deb.devuan.org/merged chimaera-backports main contrib non-free
    deb-src http://deb.devuan.org/merged chimaera-backports main contrib non-free

and ran an update and upgrade

I expected # aptitude search nano would now return a nano package with
the .bpo extendion. It did not. Whe not?

Next I tried to satisfy dependencies:

# apt-get build-dep -t testing nano
but this returns:

  E: The value 'testing' is invalid for APT::Default-Release as such 
    a release is not available in the sources
  E: Unable to find a source package for nano 

# apt-get build-dep nano-5.9
still can't find the source pacakage.

I thought the -t would override the deault stable, but instead it
seems the default value stable is negating the -t option.

--
Haines Brown