test(datetime): add daysInMonth tests (ionic-team#17558)

* fix(Datetime): correct days in month calculation

* test(DateTimeUtil): daysInMonth

* revert fn changes, keep tests

core/src/components/datetime/test/datetime.spec.ts

@@ -1,60 +1,78 @@
-import { DatetimeData, getDateValue, getLocalDateTime } from '../datetime-util';
+import { DatetimeData, daysInMonth, getDateValue, getLocalDateTime } from '../datetime-util';
 
 describe('Datetime', () => {
   describe('getDateValue()', () => {
     it('it should return the date value for the current day', () => {
       const today = new Date();
-      
+
       const dayValue = getDateValue({}, 'DD');
       const monthvalue = getDateValue({}, 'MM');
       const yearValue = getDateValue({}, 'YYYY');
-      
+
       expect(dayValue).toEqual(today.getDate());
       expect(monthvalue).toEqual(today.getMonth() + 1);
       expect(yearValue).toEqual(today.getFullYear());
     });
-    
+
     it('it should return the date value for a given day', () => {
       const date = new Date('15 October 1995');
       const dateTimeData: DatetimeData = {
         year: date.getFullYear(),
         month: date.getMonth() + 1,
         day: date.getDate()
       }
-      
+
       const dayValue = getDateValue(dateTimeData, 'DD');
       const monthvalue = getDateValue(dateTimeData, 'MM');
       const yearValue = getDateValue(dateTimeData, 'YYYY');
-      
+
       expect(dayValue).toEqual(date.getDate());
       expect(monthvalue).toEqual(date.getMonth() + 1);
       expect(yearValue).toEqual(date.getFullYear());
     });
   });
-  
+
   describe('getLocalDateTime()', () => {
     it('should format a datetime string according to the local timezone', () => {
-      
+
       const dateStringTests = [
         { expectedHourUTC: 12, input: `2019-03-02T12:08:06.601-00:00`, expectedOutput: `2019-03-02T%HOUR%:08:06.601Z` },
         { expectedHourUTC: 12, input: `2019-11-02T12:08:06.601-00:00`, expectedOutput: `2019-11-02T%HOUR%:08:06.601Z` },
         { expectedHourUTC: 8, input: `1994-12-15T13:47:20.789+05:00`, expectedOutput: `1994-12-15T%HOUR%:47:20.789Z` },
         { expectedHourUTC: 18, input: `1994-12-15T13:47:20.789-05:00`, expectedOutput: `1994-12-15T%HOUR%:47:20.789Z` },
         { expectedHourUTC: 9, input: `2019-02-14T09:00:00.000Z`, expectedOutput: `2019-02-14T%HOUR%:00:00.000Z` }
       ];
-      
+
       dateStringTests.forEach(test => {
         const convertToLocal = getLocalDateTime(test.input);
-        
+
         const timeZoneOffset = convertToLocal.getTimezoneOffset() / 60;
         const expectedDateString = test.expectedOutput.replace('%HOUR%', padNumber(test.expectedHourUTC - timeZoneOffset));
-        
+
         expect(convertToLocal.toISOString()).toEqual(expectedDateString);
       });
     });
   });
+
+  describe('daysInMonth()', () => {
+    it('should return correct days in month for month and year', () => {
+      expect(daysInMonth(1, 2019)).toBe(31);
+      expect(daysInMonth(2, 2019)).toBe(28);
+      expect(daysInMonth(3, 2019)).toBe(31);
+      expect(daysInMonth(4, 2019)).toBe(30);
+      expect(daysInMonth(5, 2019)).toBe(31);
+      expect(daysInMonth(6, 2019)).toBe(30);
+      expect(daysInMonth(7, 2019)).toBe(31);
+      expect(daysInMonth(8, 2019)).toBe(31);
+      expect(daysInMonth(9, 2019)).toBe(30);
+      expect(daysInMonth(10, 2019)).toBe(31);
+      expect(daysInMonth(11, 2019)).toBe(30);
+      expect(daysInMonth(12, 2019)).toBe(31);
+      expect(daysInMonth(2, 2020)).toBe(29);
+    });
+  });
 });
 
 function padNumber(number: number, totalLength: number = 2): string {
   return number.toString().padStart(totalLength, '0');
-}
+}