Add Get Numbers of Days of a Month (#464)

Timing-Functions/GetMonthDays.test.js

@@ -0,0 +1,19 @@
+import { getMonthDays } from './GetMonthDays'
+
+describe('Get the Days of a Month', () => {
+  it('expects to return 28', () => {
+    expect(getMonthDays(2, 2018)).toEqual(28)
+  })
+
+  it('expects to return 30', () => {
+    expect(getMonthDays(6, 254)).toEqual(30)
+  })
+
+  it('expects to return 29', () => {
+    expect(getMonthDays(2, 2024)).toEqual(29)
+  })
+
+  it('expects to throw a type error', () => {
+    expect(() => { getMonthDays(13, 2020) }).toThrow('Invalid Month Number.')
+  })
+})