nix/tests: assert commits produce new derivations

Signed-off-by: NotAShelf <raf@notashelf.dev>
Change-Id: I722e9447acfb64dd898c540c2a164a8a6a6a6964

Author: NotAShelf

nix/tests/e2e.nix

@@ -150,6 +150,7 @@ testers.runNixOSTest {
             f"curl -sf 'http://127.0.0.1:3000/api/v1/builds?evaluation_id={e2e_eval_id}' | jq -r '.items[0].drv_path'"
         ).strip()
         assert drv_path.startswith("/nix/store/"), f"Expected /nix/store/ drv_path, got '{drv_path}'"
+        e2e_drv_path = drv_path
 
         # Get the build ID for later
         e2e_build_id = machine.succeed(
@@ -203,6 +204,16 @@ testers.runNixOSTest {
             f"test $(curl -sf 'http://127.0.0.1:3000/api/v1/evaluations?jobset_id={e2e_jobset_id}' | jq '.items | length') -gt {before_count_int}",
             timeout=60
         )
+        updated_eval_id = machine.succeed(
+            f"curl -sf 'http://127.0.0.1:3000/api/v1/evaluations?jobset_id={e2e_jobset_id}' "
+            "| jq -r '.items[] | select(.status==\"completed\") | .id' | head -1"
+        ).strip()
+        updated_drv_path = machine.succeed(
+            f"curl -sf 'http://127.0.0.1:3000/api/v1/builds?evaluation_id={updated_eval_id}' "
+            "| jq -r '.items[0].drv_path'"
+        ).strip()
+        assert updated_drv_path != e2e_drv_path, \
+            "Expected the updated commit to produce a different derivation"
 
     with subtest("Queue runner builds pending derivation"):
         # Poll the E2E build until succeeded (queue-runner is already running)