output missing/substitutable derivations in eval output

tests/test_eval.py

@@ -0,0 +1,34 @@
+#!/usr/bin/env python3
+
+import subprocess
+import json
+from tempfile import TemporaryDirectory
+from pathlib import Path
+from typing import List
+
+TEST_ROOT = Path(__file__).parent.resolve()
+PROJECT_ROOT = TEST_ROOT.parent
+BIN = PROJECT_ROOT.joinpath("build", "src", "hydra-eval-jobs")
+
+
+def common_test(extra_args: List[str]) -> None:
+    with TemporaryDirectory() as tempdir:
+        cmd = [str(BIN), "--gc-roots-dir", tempdir] + extra_args
+        res = subprocess.run(
+            cmd,
+            cwd=TEST_ROOT.joinpath("assets"),
+            text=True,
+            check=True,
+            stdout=subprocess.PIPE,
+        )
+        data = json.loads(res.stdout)
+        assert len(data["builtJob"]["builds"]) == 1
+        assert len(data["substitutedJob"]["substitutes"]) >= 1
+
+
+def test_flake() -> None:
+    common_test(["--flake", ".#"])
+
+
+def test_expression() -> None:
+    common_test(["ci.nix"])