Add tests for ProjectEuler problem 20 (Jest).

Author: lvlte

Project-Euler/test/Problem020.test.js

@@ -0,0 +1,16 @@
+const factorialDigitSum = require('../Problem020')
+
+describe('Check Problem 20 - Factorial digit sum', () => {
+  it('Factorial digit sum of 10!', () => {
+    expect(factorialDigitSum(10)).toBe(27)
+  })
+
+  it('Factorial digit sum of 100!', () => {
+    expect(factorialDigitSum()).toBe(648)
+    expect(factorialDigitSum(100)).toBe(648)
+  })
+
+  it('Factorial digit sum of 1000!', () => {
+    expect(factorialDigitSum(1000)).toBe(10539)
+  })
+})