fix: factorial function (#1093)

Maths/Factorial.js

@@ -19,18 +19,18 @@ const calcRange = (num) => {
 
 const calcFactorial = (num) => {
   if (num === 0) {
-    return 'The factorial of 0 is 1.'
+    return 1
   }
   if (num < 0) {
-    return 'Sorry, factorial does not exist for negative numbers.'
+    throw Error('Sorry, factorial does not exist for negative numbers.')
   }
   if (!num) {
-    return 'Sorry, factorial does not exist for null or undefined numbers.'
+    throw Error('Sorry, factorial does not exist for null or undefined numbers.')
   }
   if (num > 0) {
     const range = calcRange(num)
     const factorial = range.reduce((a, c) => a * c, 1)
-    return `The factorial of ${num} is ${factorial}`
+    return factorial
   }
 }
 

Maths/test/Factorial.test.js

@@ -2,30 +2,20 @@ import { calcFactorial } from '../Factorial'
 
 describe('calcFactorial', () => {
   it('should return a statement for value "0"', () => {
-    expect(calcFactorial(0)).toBe('The factorial of 0 is 1.')
+    expect(calcFactorial(0)).toBe(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 throw error for "null" and "undefined"', () => {
+    expect(() => { calcFactorial(null) }).toThrow(Error)
+    expect(() => { calcFactorial(undefined) }).toThrow(Error)
   })
 
-  it('should not support negative numbers', () => {
-    const negativeFactorial = calcFactorial(-5)
-    expect(negativeFactorial).toBe(
-      'Sorry, factorial does not exist for negative numbers.'
-    )
+  it('should throw error for negative numbers', () => {
+    expect(() => { calcFactorial(-1) }).toThrow(Error)
   })
 
   it('should return the factorial of a positive number', () => {
     const positiveFactorial = calcFactorial(3)
-    expect(positiveFactorial).toBe('The factorial of 3 is 6')
+    expect(positiveFactorial).toBe(6)
   })
 })