lib/tests/release.nix: Run systems tests on OfBorg

lib/tests/release.nix

@@ -53,6 +53,9 @@ let
       echo "Running lib/tests/sources.sh"
       TEST_LIB=$PWD/lib bash lib/tests/sources.sh
 
+      echo "Running lib/tests/systems.nix"
+      [[ $(nix-instantiate --eval --strict lib/tests/systems.nix | tee /dev/stderr) == '[ ]' ]];
+
       mkdir $out
       echo success > $out/${nix.version}
     '';

lib/tests/systems.nix

@@ -1,6 +1,8 @@
 # Run:
 # [nixpkgs]$ nix-instantiate --eval --strict lib/tests/systems.nix
 # Expected output: [], or the failed cases
+#
+# OfBorg runs (approximately) nix-build lib/tests/release.nix
 let
   lib = import ../default.nix;
   mseteq = x: y: {