Add tests for Project Euler Problem 5 + minor refactor (#1691)

Project-Euler/test/Problem005.test.js

@@ -0,0 +1,12 @@
+import { expect } from 'vitest'
+import { findSmallestMultiple } from '../Problem005.js'
+
+describe.concurrent('Find smallest multiple', () => {
+  test.each([
+    [10, 2520],
+    [15, 360360],
+    [20, 232792560]
+  ])('max divisor -> %i, smallest multiple -> %i', (a, expected) => {
+    expect(findSmallestMultiple(a)).toBe(expected)
+  })
+})