Add parsing and finding the failed derivation

Signed-off-by: Marcel Müller <neikos@neikos.email>

nix-json/tests/sample-logs.rs

@@ -0,0 +1,37 @@
+use std::path::Path;
+
+use serde::Deserialize;
+
+datatest_stable::harness! {
+    {
+        test = test_failures, root = "tests/logs", pattern = r".*.failure.log"
+    },
+}
+
+#[derive(Debug, Deserialize)]
+struct FailureInfoHeader {
+    failed_derivations: Vec<String>,
+}
+
+fn test_failures(_path: &Path, content: String) -> datatest_stable::Result<()> {
+    let (header, content) = content.split_once("------").unwrap();
+
+    let header: FailureInfoHeader = serde_json::from_str(header).unwrap();
+
+    let build_state = nix_json::helpers::NixBuildState::from_log_lines(content)?;
+
+    assert!(build_state.is_failed());
+
+    for drv in header.failed_derivations {
+        let state = build_state
+            .get_derivation(&drv)
+            .unwrap_or_else(|| panic!("Expected {drv} to be present in build state"));
+
+        assert!(
+            state.is_failed(),
+            "derivation {drv} was found, but it was not marked as failed"
+        );
+    }
+
+    Ok(())
+}