toBe() for basic equality assertions

Let's start with basic equality tests.

For exact matches (same as 1 === 1 in regular JavaScript code), you can use .toBe(expectedValue).

test('basic equality', () => {
  const result = 2 + 2;
  expect(result).toBe(4);

  expect(0).toBe(0);
});

Greater than / less than

Another common thing to do when checking numbers is to do less than (1 < 2) or greater than (2 > 1).

You can do this with these functions in Jest and Vitest:

• toBeGreaterThan(x)
• toBeGreaterThanOrEqual(x)
• toBeLessThan(x)
• toBeLessThanOrEqual(x)

test('comparison matchers', () => {
  const score = 85;
  expect(score).toBeGreaterThan(80);
  expect(score).toBeGreaterThanOrEqual(
    85
  );
  expect(score).toBeLessThan(100);
  expect(score).toBeLessThanOrEqual(85);

  // note you can also do this:
  expect(score > 80).toBe(true);
});

Testing floating points (toBeCloseTo)

Numbers are not always precise in JavaScript. The famous example is 0.1 + 0.1 + 0.1 in Javascript is a little bit bigger than 0.3!

This test will fail:

expect(0.1 + 0.1 + 0.1).toBe(0.3); // ❌ fails
// this will fail, with an error such as:
// "expected 0.30000000000000004 to be 0.3"

For those numbers, you can use .toBeCloseTo(0.3)

It also takes a 2nd argument so you can define how many decimals to compare to. The default is 2 btw

test('showing toBeCloseTo precision argument', () => {
  const result = 1 / 3; // 0.3333333333333333...

  // These pass - checking fewer decimal places
  expect(result).toBeCloseTo(0.33, 2); // 2 decimal places: 0.33
  expect(result).toBeCloseTo(0.333, 3); // 3 decimal places: 0.333
  expect(result).toBeCloseTo(0.3333, 4); // 4 decimal places: 0.3333

  // This would fail - too precise for the actual value
  // expect(result).toBeCloseTo(0.34, 2); // ❌ would fail
});

Other number comparisons

The other special number matcher to be aware of is the .toBeNaN() function

test('special number values', () => {
  expect(NaN).toBeNaN();
});

You might also need to compare positive and negative infinity. This can be done with the .toBe() function

test('infinity checks', () => {
  expect(Infinity).toBe(Infinity);
  expect(-Infinity).toBe(-Infinity);
});