add tests for showing help

package.nix

@@ -24,6 +24,7 @@
 , libgit2
 , libseccomp
 , libsodium
+, man
 , lowdown
 , mdbook
 , mdbook-linkcheck
@@ -213,6 +214,7 @@ in {
     git
     mercurial
     openssh
+    man # for testing `nix-* --help`
   ] ++ lib.optionals (doInstallCheck || enableManual) [
     jq # Also for custom mdBook preprocessor.
   ] ++ lib.optional stdenv.hostPlatform.isLinux util-linux

tests/functional/help.sh

@@ -0,0 +1,79 @@
+source common.sh
+
+clearStore
+
+# test help output
+
+nix-build --help
+nix-shell --help
+
+nix-env --help
+nix-env --install --help
+nix-env --upgrade --help
+nix-env --uninstall --help
+nix-env --set --help
+nix-env --set-flag --help
+nix-env --query --help
+nix-env --switch-profile --help
+nix-env --list-generations --help
+nix-env --delete-generations --help
+nix-env --switch-generation --help
+nix-env --rollback --help
+
+nix-store --help
+nix-store --realise --help
+nix-store --serve --help
+nix-store --gc --help
+nix-store --delete --help
+nix-store --query --help
+nix-store --add --help
+nix-store --add-fixed --help
+nix-store --verify --help
+nix-store --verify-path --help
+nix-store --repair-path --help
+nix-store --dump --help
+nix-store --restore --help
+nix-store --export --help
+nix-store --import --help
+nix-store --optimise --help
+nix-store --read-log --help
+nix-store --dump-db --help
+nix-store --load-db --help
+nix-store --print-env --help
+nix-store --generate-binary-cache-key --help
+
+nix-channel --help
+nix-collect-garbage --help
+nix-copy-closure --help
+nix-daemon --help
+nix-hash --help
+nix-instantiate --help
+nix-prefetch-url --help
+
+function subcommands() {
+  jq -r '
+def recurse($prefix):
+  if .commands then
+    .commands | to_entries[] | .key as $k |
+    ($prefix + " " + $k) as $newPrefix |
+    if .value | has("commands") then
+      (.value | recurse($newPrefix))
+    else
+      $newPrefix
+    end
+  else
+    $prefix
+  end;
+
+.args.commands | to_entries[] | .key as $cmd |
+  if .value | has("commands") then
+    (.value | recurse($cmd))
+  else
+    $cmd
+  end
+'
+}
+
+nix __dump-cli | subcommands | while IFS= read -r cmd; do
+    nix $cmd --help
+done

tests/functional/local.mk

@@ -129,7 +129,8 @@ nix_tests = \
   read-only-store.sh \
   nested-sandboxing.sh \
   impure-env.sh \
-  debugger.sh
+  debugger.sh \
+	help.sh
 
 ifeq ($(HAVE_LIBCPUID), 1)
   nix_tests += compute-levels.sh