date: add tests for --resolution flag

Author: Banzobotic

tests/by-util/test_date.rs

@@ -745,3 +745,36 @@ fn test_date_empty_tz_time() {
         .succeeds()
         .stdout_only("Thu Jan  1 00:00:00 UTC 1970\n");
 }
+
+#[test]
+fn test_date_resolution() {
+    // Test that --resolution flag returns a floating point number by default
+    new_ucmd!()
+        .arg("--resolution")
+        .succeeds()
+        .stdout_str_check(|s| s.trim().parse::<f64>().is_ok());
+
+    // Test that --resolution flag can be passed twice to match gnu
+    new_ucmd!()
+        .arg("--resolution")
+        .arg("--resolution")
+        .succeeds()
+        .stdout_str_check(|s| s.trim().parse::<f64>().is_ok());
+
+    // Test that can --resolution output can be formatted as a date
+    new_ucmd!()
+        .arg("--resolution")
+        .arg("-Iseconds")
+        .succeeds()
+        .stdout_only("1970-01-01T00:00:00+00:00\n");
+}
+
+#[test]
+fn test_date_resolution_no_combine() {
+    // Test that date fails when --resolution flag is passed with date flag
+    new_ucmd!()
+        .arg("--resolution")
+        .arg("-d")
+        .arg("2025-01-01")
+        .fails();
+}