Our first tests

As a reminder, here’s our final implementation:

export const fizzBuzz = (i: number): string => {
  if (i % 15 === 0) {
    return "fizzbuzz";
  }
  if (i % 3 === 0) {
    return "fizz";
  }
  if (i % 5 === 0) {
    return "buzz";
  }
  return i.toString(10);
};

Note that we export the fizzbuzz function, so we can import it later on.

Writing some tests

Writing a main and checking the output by hand is not fun, so let’s write some tests instead:

import { fizzBuzz } from "./fizzbuzz.ts";
import { assertEquals } from "@std/assert";

Deno.test("Print 'fizz' when divisible by 3", () => {
  assertEquals(fizzBuzz(3), "fizz");
  assertEquals(fizzBuzz(6), "fizz");
  assertEquals(fizzBuzz(9), "fizz");
});

Deno.test("Print 'buzz' when divisible by 5", () => {
  assertEquals(fizzBuzz(5), "buzz");
  assertEquals(fizzBuzz(10), "buzz");
  assertEquals(fizzBuzz(20), "buzz");
});

Deno.test("Print 'fizzbuzz' when divisible by 15", () => {
  assertEquals(fizzBuzz(15), "fizzbuzz");
  assertEquals(fizzBuzz(30), "fizzbuzz");
});

Deno.test("Print number otherwise", () => {
  assertEquals(fizzBuzz(2), "2");
  assertEquals(fizzBuzz(4), "4");
});

Running the tests

$ deno test fizzbuzz_test.ts

Check fizzbuzz_test.ts
running 4 tests from ./fizzbuzz_test.ts
Print 'fizz' when divisible by 3 ... ok
Print 'buzz' when divisible by 5 ... ok
Print 'fizzbuzz' when divisible by 15 ... ok
Print number otherwise ... ok

ok | 4 passed | 0 failed (4ms)