initial version

nix-tests.nix

@@ -0,0 +1,27 @@
+pkgs: tests: let
+  formatValue = val:
+    if (builtins.isList val || builtins.isAttrs val)
+    then builtins.toJSON val
+    else builtins.toString val;
+  resultToString = {
+    name,
+    expected,
+    result,
+  }: ''
+    ${name} failed: expected ${formatValue expected}, but got ${
+      formatValue result
+    }
+  '';
+  results = pkgs.lib.runTests (tests pkgs);
+in
+  if results != []
+  then builtins.throw (builtins.concatStringsSep "\n" (map resultToString results))
+  ## TODO: The derivation below is preferable but "nix flake check" hangs with it:
+  ##       (it's preferable because "examples/many-failures" would then show all errors.)
+  # pkgs.runCommand "nix-flake-tests-failure" { } ''
+  #   cat <<EOF
+  #   ${builtins.concatStringsSep "\n" (map resultToString results)}
+  #   EOF
+  #   exit 1
+  # ''
+  else pkgs.runCommand "nix-flake-tests-success" {} "echo > $out"