add test case for extended timestamp

tests/zip_extended_timestamp.rs

@@ -0,0 +1,19 @@
+use std::io;
+use zip::ZipArchive;
+
+#[test]
+fn test_extended_timestamp() {
+    let mut v = Vec::new();
+    v.extend_from_slice(include_bytes!("../tests/data/extended_timestamp.zip"));
+    let mut archive = ZipArchive::new(io::Cursor::new(v)).expect("couldn't open test zip file");
+
+    for field in archive.by_name("test.txt").unwrap().extra_data_fields() {
+        match field {
+            zip::ExtraField::ExtendedTimestamp(ts) => {
+                assert!(ts.ac_time().is_none());
+                assert!(ts.cr_time().is_none());
+                assert_eq!(*ts.mod_time().unwrap(), 1714635025);
+            },
+        }
+    }
+}