lukas@wolfgang ~/s/depot (canon) [1]> nix repl . Welcome to Nix version 2.3.10. Type :? for help. Loading '.'... Added 19 variables. nix-repl> nix.readTree { __functor = «lambda @ /home/lukas/src/depot/nix/readTree/default.nix:80:16»; __readTree = [ ... ]; tests = «derivation /nix/store/n302bv981765cnd2dd30w47fn7rkgy4i-testsuite-readTree-successful.drv»; } nix-repl> nix.readTree.tests «derivation /nix/store/n302bv981765cnd2dd30w47fn7rkgy4i-testsuite-readTree-successful.drv» nix-repl> :b nix.readTree.tests [1 built] this derivation produced the following outputs: out -> /nix/store/ybcgvx7icybg71y7qrx539ngs2h5fcwl-testsuite-readTree-successful lukas@wolfgang ~/s/depot (canon)> nix-build -A nix.readTree.tests error: the expression selected by the selection path 'nix.readTree.tests' should be a set but is a function lukas@wolfgang ~/s/depot (canon) [1]>