feat: add quarter in calendar date

src/CalendarDate.ts

@@ -424,4 +424,17 @@ export class CalendarDate {
       )
     );
   }
+
+  /**
+   * The quarter of the year (1-4) based on the month of the date.
+   *
+   * Quarter breakdown:
+   * - 1st Quarter: January to March (1-3)
+   * - 2nd Quarter: April to June (4-6)
+   * - 3rd Quarter: July to September (7-9)
+   * - 4th Quarter: October to December (10-12)
+   */
+  public get quarter(): number {
+    return Math.floor((this.month - 1) / 3) + 1;
+  }
 }

test/CalendarDate.test.ts

@@ -1411,4 +1411,41 @@ describe('CalendarDate', () => {
       }
     });
   });
+
+  describe('Test of quarter', () => {
+    test('Result is always between 1 and 4', () => {
+      fc.assert(
+        fc.property(
+          fc.integer({ min: 200, max: 9900 }),
+          fc.integer({ min: 1, max: 12 }),
+          fc.integer({ min: 1, max: 31 }),
+          (year, month, day) => {
+            // Arrange
+            const calendarDate = new CalendarDate(year, month, ensureValidDay(year, month, day));
+
+            // Act
+            const quarter = calendarDate.quarter;
+
+            // Assert
+            expect(quarter).toBeLessThan(5);
+            expect(quarter).toBeGreaterThan(0);
+          },
+        ),
+      );
+    });
+    test('Correct quarter for each month', () => {
+      expect(new CalendarDate(2023, 1, 1).quarter).toBe(1);
+      expect(new CalendarDate(2023, 2, 1).quarter).toBe(1);
+      expect(new CalendarDate(2023, 3, 1).quarter).toBe(1);
+      expect(new CalendarDate(2023, 4, 1).quarter).toBe(2);
+      expect(new CalendarDate(2023, 5, 1).quarter).toBe(2);
+      expect(new CalendarDate(2023, 6, 1).quarter).toBe(2);
+      expect(new CalendarDate(2023, 7, 1).quarter).toBe(3);
+      expect(new CalendarDate(2023, 8, 1).quarter).toBe(3);
+      expect(new CalendarDate(2023, 9, 1).quarter).toBe(3);
+      expect(new CalendarDate(2023, 10, 1).quarter).toBe(4);
+      expect(new CalendarDate(2023, 11, 1).quarter).toBe(4);
+      expect(new CalendarDate(2023, 12, 1).quarter).toBe(4);
+    });
+  });
 });