LibJS+LibUnicode: Generate missing patterns with fractionalSecondDigits

TR-35's Matching Skeleton algorithm dictates how user requests including
fractional second digits should be handled when the CLDR format pattern
does not include that field. When the format pattern contains {second},
but does not contain {fractionalSecondDigits}, generate a second pattern
which appends "{decimal}{fractionalSecondDigits}" to the {second} field.

1 files changed, 9 insertions, 3 deletions

diff --git a/Userland/Libraries/LibJS/Tests/builtins/Intl/DateTimeFormat/DateTimeFormat.prototype.resolvedOptions.js b/Userland/Libraries/LibJS/Tests/builtins/Intl/DateTimeFormat/DateTimeFormat.prototype.resolvedOptions.js
index cb9ff39372..da70832e14 100644
--- a/Userland/Libraries/LibJS/Tests/builtins/Intl/DateTimeFormat/DateTimeFormat.prototype.resolvedOptions.js
+++ b/Userland/Libraries/LibJS/Tests/builtins/Intl/DateTimeFormat/DateTimeFormat.prototype.resolvedOptions.js
@@ -1,6 +1,3 @@
-// NOTE: We cannot yet test the fractionalSecondDigits option. There aren't any patterns in the CLDR
-//       with this field ('S' in https://unicode.org/reports/tr35/tr35-dates.html#dfst-second). We
-//       will need to figure out how this field should be generated.
 describe("correct behavior", () => {
     test("length is 0", () => {
         expect(Intl.DateTimeFormat.prototype.resolvedOptions).toHaveLength(0);
@@ -179,6 +176,15 @@ describe("correct behavior", () => {
         });
     });
 
+    test("fractionalSecondDigits", () => {
+        [1, 2, 3].forEach(fractionalSecondDigits => {
+            const en = new Intl.DateTimeFormat("en", {
+                fractionalSecondDigits: fractionalSecondDigits,
+            });
+            expect(en.resolvedOptions().fractionalSecondDigits).toBe(fractionalSecondDigits);
+        });
+    });
+
     test("timeZoneName", () => {
         ["short", "long"].forEach(timeZoneName => {
             const en = new Intl.DateTimeFormat("en", { timeZoneName: timeZoneName });