Fix #1600: add end-2-end test of hix project initialization and flakes development shell

Author: yvan-sraka

.buildkite/pipeline.yml

@@ -50,3 +50,12 @@ steps:
       - nix-instantiate release.nix -A required-unstable-ghc8107-x86_64-darwin-native --show-trace --builders ''
     agents:
       system: x86_64-linux
+
+  - label: 'End-2-end test of hix project initialization and flakes development shell'
+    command:
+      - cabal unpack hello
+      - cd hello-*
+      - nix run "github:input-output-hk/haskell.nix#hix" -- init
+      - nix develop -c cabal build
+    agents:
+      system: x86_64-linux