test: add variation test for WORKWEEKSTART

tests/reach_variations_test.ts

@@ -56,6 +56,23 @@ Deno.test("Variation: Recurring Weekly (Multi-day: MO,TU,WE,TH,FR)", () => {
   assert(results.some(r => r.start.includes("2026-01-20"))); // Tuesday
 });
 
+Deno.test("Variation: Recurring with WORKWEEKSTART (Outlook style)", () => {
+  const icsEvent = {
+    summary: "Outlook Style Meeting",
+    start: "2026-01-20T08:30:00",
+    rrule: {
+        frequency: "WEEKLY",
+        interval: 1,
+        byday: "TU",
+        workweekstart: "MO"
+    }
+  };
+  
+  const results = expandRecurrences(icsEvent, 30, TEST_NOW);
+  assert(results.length > 0);
+  assert(results[0].start.includes("2026-01-20"));
+});
+
 Deno.test("Variation: Recurring with EXDATE (Exclusion)", () => {
   const icsEvent = {
     summary: "HPE-Veeam check-in",