test: add tests for numberWithCommas

src/utils/numberWithCommas.test.ts

@@ -0,0 +1,33 @@
+import numberWithCommas from './numberWithCommas'
+
+test('leaves single-digit values alone', () => {
+  for (let i = 0; i <= 9; i++) {
+    expect(numberWithCommas(i)).toEqual(`${i}`)
+  }
+})
+
+test('leaves double-digit values alone', () => {
+  for (let i = 10; i <= 99; i++) {
+    expect(numberWithCommas(i)).toEqual(`${i}`)
+  }
+})
+
+test('leaves triple-digit values alone', () => {
+  for (let i = 100; i <= 999; i++) {
+    expect(numberWithCommas(i)).toEqual(`${i}`)
+  }
+})
+
+test('inserts a grouping separator between the hundreds and thousands places', () => {
+  expect(numberWithCommas(1000)).toEqual('1,000')
+  expect(numberWithCommas(1234)).toEqual('1,234')
+  expect(numberWithCommas(9999)).toEqual('9,999')
+  expect(numberWithCommas(58763)).toEqual('58,763')
+})
+
+test('inserts grouping separators at all relevant places', () => {
+  expect(numberWithCommas(1000000000)).toEqual('1,000,000,000')
+  expect(numberWithCommas(1234567890)).toEqual('1,234,567,890')
+  expect(numberWithCommas(9999999999)).toEqual('9,999,999,999')
+  expect(numberWithCommas(5876319472)).toEqual('5,876,319,472')
+})