tests/date: add test date strftime O and E modifier

Author: tobyw21

tests/by-util/test_date.rs

@@ -1965,7 +1965,6 @@ fn test_date_strftime_flag_on_composite() {
 }
 
 #[test]
-#[ignore = "https://github.com/uutils/coreutils/issues/11656 — GNU date strips the `O` strftime modifier in C locale (e.g. `%Om` -> `%m`); uutils leaks it as literal `%om`."]
 fn test_date_strftime_o_modifier() {
     // In C locale the `O` modifier is a no-op (alternative numeric symbols).
     // GNU renders `%Om` as `06` for June; uutils renders it as the literal `%Om`.
@@ -1979,6 +1978,20 @@ fn test_date_strftime_o_modifier() {
         .stdout_is("06-24-12\n");
 }
 
+#[test]
+fn test_date_strftime_e_modifier() {
+    // In C locale the `E` modifier is a no-op (alternative era).
+    // GNU does not render `%Em`; uutils renders it as the literal `%Em` as `06` for June.
+    new_ucmd!()
+        .env("LC_ALL", "C")
+        .env("TZ", "UTC")
+        .arg("-d")
+        .arg("2024-06-15")
+        .arg("+%Em-%Ey-%El")
+        .succeeds()
+        .stdout_is("06-24-12\n");
+}
+
 #[test]
 #[ignore = "https://github.com/uutils/parse_datetime/issues/280 — GNU date accepts bare timezone abbreviations (UT, GMT, ...) meaning `now in that TZ`; parse_datetime rejects them."]
 fn test_date_bare_timezone_abbreviation() {