my solution

src/splitInteger.js

@@ -20,4 +20,6 @@ function splitInteger(value, numberOfParts) {
   return parts;
 }
 
+// console.log(splitInteger(12, 0));
+
 module.exports = splitInteger;

src/splitInteger.test.js

@@ -4,18 +4,61 @@
 
 test(`should split a number into equal parts
   if a value is divisible by a numberOfParts`, () => {
-
+  expect(splitInteger(12, 3)).toEqual([4, 4, 4]);
 });
 
 test(`should return a part equals to a value
   when splitting into 1 part`, () => {
-
+  expect(splitInteger(8, 1)).toEqual([8]);
 });
 
 test('should sort parts ascending if they are not equal', () => {
+  expect(splitInteger(8, 3)).toEqual([2, 3, 3]);
+  expect(splitInteger(17, 4)).toEqual([4, 4, 4, 5]);
+});
+
+test('should always return an array of length numberOfParts', () => {
+  expect(splitInteger(32, 6)).toHaveLength(6);
+});
+
+test('should return an array with integer in every case', () => {
+  expect(splitInteger(5, 3).every(Number.isInteger)).toBe(true);
+  expect(splitInteger(5, 10).every(Number.isInteger)).toBe(true);
+});
+
+test('should sum of parts always equal to value', () => {
+  const value = 17;
 
+  expect(splitInteger(value, 3).reduce((a, b) => a + b, 0)).toBe(value);
+  expect(splitInteger(value, 10).reduce((a, b) => a + b, 0)).toBe(value);
+  expect(splitInteger(value, 1).reduce((a, b) => a + b, 0)).toBe(value);
 });
 
-test('should add zeros if value < numberOfParts', () => {
+test('should deference between max and min part to be <= 1', () => {
+  if (splitInteger().length > 0) {
+    expect(Math.max(...splitInteger(17, 3)) - Math.min(...splitInteger(17, 3)))
+      .toBeLessThanOrEqual(1);
+
+    expect(Math.max(...splitInteger(17, 10)) - Math.min(...splitInteger(17, 10)))
+      .toBeLessThanOrEqual(1);
+
+    expect(Math.max(...splitInteger(17, 4)) - Math.min(...splitInteger(17, 4)))
+      .toBeLessThanOrEqual(1);
+  }
+});
+
+test('should return an array is sorted in non-decreasing order', () => {
+  expect(splitInteger(32, 6)).toEqual(splitInteger(32, 6).slice()
+    .sort((a, b) => a - b));
+
+  expect(splitInteger(17, 4)).toEqual(splitInteger(17, 4).slice()
+    .sort((a, b) => a - b));
+
+  expect(splitInteger(8, 1)).toEqual(splitInteger(8, 1).slice()
+    .sort((a, b) => a - b));
+});
 
+test('should return an array with amount of larger parts to equal value % numberOfParts if not evenly divisible ', () => {
+  expect(splitInteger(17, 4).filter((part) => part === 5)).toHaveLength(1);
+  expect(splitInteger(32, 6).filter((part) => part === 6)).toHaveLength(2);
 });