Add method addDays to ValidDate

package.json

@@ -1,6 +1,6 @@
 {
   "name": "valid-objects-ts",
-  "version": "1.0.6",
+  "version": "1.0.7",
   "main": ".dist/index.js",
   "types": ".dist/index.d.ts",
   "repository": "[email protected]:Travelport-Czech/valid-objects-ts.git",

src/validObjects/ValidDate.test.ts

@@ -33,4 +33,18 @@ describe('ValidDate', () => {
     const date4 = new ValidDate('2017-12-24')
     expect(date.diffInDays(date4)).to.equal(365)
   })
+
+  it('subtract days', () => {
+    const date = new ValidDate('2018-12-24')
+    expect(date.subtractDays(0).toString()).to.equal('2018-12-24')
+    expect(date.subtractDays(1).toString()).to.equal('2018-12-23')
+    expect(date.subtractDays(100).toString()).to.equal('2018-09-15')
+  })
+
+  it('add days', () => {
+    const date = new ValidDate('2018-12-24')
+    expect(date.addDays(0).toString()).to.equal('2018-12-24')
+    expect(date.addDays(1).toString()).to.equal('2018-12-25')
+    expect(date.addDays(100).toString()).to.equal('2019-04-03')
+  })
 })

src/validObjects/ValidDate.ts

@@ -69,6 +69,14 @@ export class ValidDate {
     )
   }
 
+  public readonly addDays = (days: number): ValidDate => {
+    return new ValidDate(
+      this.moment()
+        .add(days, 'days')
+        .format(formatSystemDate)
+    )
+  }
+
   public readonly diffInDays = (date: ValidDate): number => {
     return this.moment().diff(date.moment(), 'days')
   }