Add tests to Math (#423)

* Add prettier config

* test: add test to check for absolute function

* chore: es5 to es6

* test: add test to check mean function

* test: add test for sum of digit

* test: add test for factorial

* test: add test for fibonnaci

* test: add test for find HCF

* test: add test for lcm

* test: add gridget test

* test: add test for mean square error

* test: add test for modular binary exponentiation

* test: add tests for palindrome

* test: add test for pascals triangle

* test: add tests for polynomial

* test: add tests for prime check

* test: add tests for reverse polish notation

* test: add tests for sieve of eratosthenes

* test: add tests for pi estimation monte carlo method

* chore: move tests to test folder

* chore: fix standardjs errors

Maths/test/Factorial.test.js

@@ -0,0 +1,35 @@
+import { calcFactorial } from '../Factorial'
+
+describe('calcFactorial', () => {
+  it('is a function', () => {
+    expect(typeof calcFactorial).toEqual('function')
+  })
+
+  it('should return a statement for value "0"', () => {
+    expect(calcFactorial(0)).toBe('The factorial of 0 is 1.')
+  })
+
+  it('should return a statement for "null" and "undefined"', () => {
+    const nullFactorial = calcFactorial(null)
+    const undefinedFactorial = calcFactorial(undefined)
+
+    expect(nullFactorial).toBe(
+      'Sorry, factorial does not exist for null or undefined numbers.'
+    )
+    expect(undefinedFactorial).toBe(
+      'Sorry, factorial does not exist for null or undefined numbers.'
+    )
+  })
+
+  it('should not support negative numbers', () => {
+    const negativeFactorial = calcFactorial(-5)
+    expect(negativeFactorial).toBe(
+      'Sorry, factorial does not exist for negative numbers.'
+    )
+  })
+
+  it('should return the factorial of a positive number', () => {
+    const positiveFactorial = calcFactorial(3)
+    expect(positiveFactorial).toBe('The factorial of 3 is 6')
+  })
+})