Test cases project euler 9 (TheAlgorithms#1571)

* 📦 NEW: Added solution for ProjectEuler-007

* 🐛 FIX: Spelling mistake fixes

* 👌 IMPROVE: changed variable name from `inc` to `candidateValue` and thrown error in case of invalid input

* 👌 IMPROVE: Modified the code

* 👌 IMPROVE: Added test case for ProjectEuler Problem001

* 👌 IMPROVE: Added test cases for Project Euler Problem 4

* 👌 IMPROVE: auto prettier fixes

* 👌 IMPROVE: Added test cases for project euler problem 9

* Updated Documentation in README.md

* Updated Documentation in README.md

---------

Co-authored-by: Omkarnath Parida <omkarnath.parida@yocket.in>
Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>

Author: 3 people

Project-Euler/test/Problem009.test.js

@@ -0,0 +1,8 @@
+import { findSpecialPythagoreanTriplet } from '../Problem009.js'
+
+describe('Pythagorean Triplet', () => {
+  // Project Euler Condition Check
+  test('the multiplication of the pythagorean triplet where a + b + c = 1000', () => {
+    expect(findSpecialPythagoreanTriplet()).toBe(31875000)
+  })
+})