Merge pull request #597 from Masa-Shin/fix-maths-is-divisible

Fix Maths/IsDivisible

Maths/IsDivisible.js

@@ -1,11 +1,11 @@
 // Checks if a number is divisible by another number.
 
-const isDivisible = (num1, num2) => {
-  if (isNaN(num1) || isNaN(num2) || num1 == null || num2 == null) {
-    return 'All parameters have to be numbers'
+export const isDivisible = (num1, num2) => {
+  if (!Number.isFinite(num1) || !Number.isFinite(num2)) {
+    throw new TypeError('Expected a number')
   }
   if (num2 === 0) {
-    return 'Not possible to divide by zero'
+    return false
   }
   return num1 % num2 === 0
 }

Maths/test/IsDivisible.test.js

@@ -0,0 +1,39 @@
+import { isDivisible } from '../IsDivisible'
+
+describe('isDivisible', () => {
+  const testCases = [
+    [0, 1, true],
+    [0, 2, true],
+    [1, 1, true],
+    [1, 2, false],
+    [2, 1, true],
+    [4, 4, true],
+    [16, 4, true],
+    [36978235, 5, true],
+    [36978235, 4, false],
+    [4.5, 1.5, true],
+    [4.5, 1.2, false],
+    [5, 0, false],
+    [5, -0, false]
+  ]
+
+  test.each(testCases)('if parameters are (%i, %i) it returns %p', (dividend, divisor, expected) => {
+    expect(isDivisible(dividend, divisor)).toBe(expected)
+  })
+
+  const errorCases = [
+    [NaN, NaN],
+    [NaN, 1],
+    [1, NaN],
+    ['1', 1],
+    [1, '1'],
+    [1, true],
+    [false, 2]
+  ]
+
+  test.each(errorCases)('throws an error if parameters are (%p, %p)', (dividend, divisor) => {
+    expect(() => {
+      isDivisible(dividend, divisor)
+    }).toThrow()
+  })
+})