test(journaldriver): Add test for serialising timestamps

Change-Id: I5b769f5974546fd4f4f853111bd17c9d22d73a5e
Reviewed-on: https://cl.tvl.fyi/c/depot/+/5310
Tested-by: BuildkiteCI
Autosubmit: tazjin <tazjin@tvl.su>
Reviewed-by: sterni <sternenseemann@systemli.org>

ops/journaldriver/src/tests.rs

@@ -21,6 +21,28 @@ fn test_text_entry_serialization() {
     )
 }
 
+#[test]
+fn test_timestamped_entry_serialization() {
+    let timestamp: DateTime<Utc> = "1952-10-07T12:00:00Z".to_string().parse().unwrap();
+    let entry = LogEntry {
+        labels: Value::Null,
+        timestamp: Some(timestamp),
+        payload: Payload::TextPayload {
+            text_payload: "test entry".into(),
+        },
+        severity: None,
+    };
+
+    let expected =
+        "{\"labels\":null,\"timestamp\":\"1952-10-07T12:00:00Z\",\"textPayload\":\"test entry\"}";
+    let result = to_string(&entry).expect("serialization failed");
+
+    assert_eq!(
+        expected, result,
+        "Plain text payload should serialize correctly"
+    )
+}
+
 #[test]
 fn test_json_entry_serialization() {
     let entry = LogEntry {
@@ -37,7 +59,7 @@ fn test_json_entry_serialization() {
     let expected = "{\"labels\":null,\"jsonPayload\":{\"message\":\"JSON test\"}}";
     let result = to_string(&entry).expect("serialization failed");
 
-    assert_eq!(expected, result, "JSOn payload should serialize correctly")
+    assert_eq!(expected, result, "JSON payload should serialize correctly")
 }
 
 #[test]