merge: Improve Mean method (#874)

Maths/test/AverageMean.test.js

@@ -4,8 +4,18 @@ describe('Tests for average mean', () => {
   it('should be a function', () => {
     expect(typeof mean).toEqual('function')
   })
+
+  it('should throw error for invalid input', () => {
+    expect(() => mean(123)).toThrow()
+  })
+
   it('should return the mean of an array of numbers', () => {
     const meanFunction = mean([1, 2, 4, 5])
     expect(meanFunction).toBe(3)
   })
+
+  it('should return the mean of an array of numbers', () => {
+    const meanFunction = mean([10, 40, 100, 20])
+    expect(meanFunction).toBe(42.5)
+  })
 })