chore: Strings: Credit Card Validation (#830)

* Add credit card number validator

- Validates the credit card number based on Luhn algorithm

* Test Cases: ValidateCreditCard

* Auto-update DIRECTORY.md

* Fix: Spell check

* Add references and move const inside function

* Add comments

* Fix trailing spaces

* Add short description

* Remove trailing spaces

Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>

String/test/ValidateCreditCard.test.js

@@ -0,0 +1,39 @@
+import { validateCreditCard } from '../ValidateCreditCard'
+
+describe('Validate credit card number', () => {
+  it('should throw error if card number is boolean', () => {
+    const invalidCC = true
+    expect(() => validateCreditCard(invalidCC)).toThrow(
+      'The given value is not a string'
+    )
+  })
+  it('returns true if the credit card number is valid', () => {
+    const validCreditCard = '4111111111111111'
+    const validationResult = validateCreditCard(validCreditCard)
+    expect(validationResult).toBe(true)
+  })
+  it('should throw an error on non-numeric character in given credit card number', () => {
+    const nonNumericCCNumbers = ['123ABCDEF', 'ABCDKDKD', 'ADS232']
+    nonNumericCCNumbers.forEach(nonNumericCC => expect(() => validateCreditCard(nonNumericCC)).toThrow(
+      `${nonNumericCC} is an invalid credit card number because ` + 'it has nonnumerical characters.'
+    ))
+  })
+  it('should throw an error on credit card with invalid length', () => {
+    const ccWithInvalidLength = ['41111', '4111111111111111111111']
+    ccWithInvalidLength.forEach(invalidCC => expect(() => validateCreditCard(invalidCC)).toThrow(
+      `${invalidCC} is an invalid credit card number because ` + 'of its length.'
+    ))
+  })
+  it('should throw an error on credit card with invalid start substring', () => {
+    const ccWithInvalidStartSubstring = ['12345678912345', '23456789123456', '789123456789123', '891234567891234', '912345678912345', '31345678912345', '32345678912345', '33345678912345', '38345678912345']
+    ccWithInvalidStartSubstring.forEach(invalidCC => expect(() => validateCreditCard(invalidCC)).toThrow(
+      `${invalidCC} is an invalid credit card number because ` + 'of its first two digits.'
+    ))
+  })
+  it('should throw an error on credit card with luhn check fail', () => {
+    const invalidCCs = ['411111111111111', '371211111111111', '49999999999999']
+    invalidCCs.forEach(invalidCC => expect(() => validateCreditCard(invalidCC)).toThrow(
+      `${invalidCC} is an invalid credit card number because ` + 'it fails the Luhn check.'
+    ))
+  })
+})