Utilizarea regulilor de potrivire

Jest uses "matchers" to let you test values in different ways. This document will introduce some commonly used matchers. For the full list, see the expect API doc.

Validatori comuni

Cel mai simplu mod de a testa o valoare este cu egalitatea exactă.

test('two plus two is four', () => {
  expect(2 + 2).toBe(4);
});

In this code, expect(2 + 2) returns an "expectation" object. De obicei nu veţi face mult cu aceste obiecte cu excepţia că veți apela validatori pe ele. In this code, .toBe(4) is the matcher. Când Jest se execută, el urmărește toți validatorii eșuați astfel încât să poată afișa frumos mesajele de eroare.

toBe uses Object.is to test exact equality. If you want to check the value of an object, use toEqual:

test('object assignment', () => {
  const data = {one: 1};
  data['two'] = 2;
  expect(data).toEqual({one: 1, two: 2});
});

toEqual recursively checks every field of an object or array.

tip

toEqual ignores object keys with undefined properties, undefined array items, array sparseness, or object type mismatch. To take these into account use toStrictEqual instead.

You can also test for the opposite of a matcher using not:

test('adding positive numbers is not zero', () => {
  for (let a = 1; a < 10; a++) {
    for (let b = 1; b < 10; b++) {
      expect(a + b).not.toBe(0);
    }
  }
});

Adevăr

In tests, you sometimes need to distinguish between undefined, null, and false, but you sometimes do not want to treat these differently. Jest conţine utillitare care vă permit să fiți expliciți despre ceea ce doriți.

• toBeNull matches only null
• toBeUndefined matches only undefined
• toBeDefined is the opposite of toBeUndefined
• toBeTruthy matches anything that an if statement treats as true
• toBeFalsy matches anything that an if statement treats as false

De exemplu:

test('null', () => {
  const n = null;
  expect(n).toBeNull();
  expect(n).toBeDefined();
  expect(n).not.toBeUndefined();
  expect(n).not.toBeTruthy();
  expect(n).toBeFalsy();
});

test('zero', () => {
  const z = 0;
  expect(z).not.toBeNull();
  expect(z).toBeDefined();
  expect(z).not.toBeUndefined();
  expect(z).not.toBeTruthy();
  expect(z).toBeFalsy();
});

Ar trebui să utilizaţi validatorul care corespunde cel mai exact cu ceea ce dorești să facă codul tău.

Numere

Majoritatea modurilor de comparare a numerelor au validatori echivalenţi.

test('two plus two', () => {
  const value = 2 + 2;
  expect(value).toBeGreaterThan(3);
  expect(value).toBeGreaterThanOrEqual(3.5);
  expect(value).toBeLessThan(5);
  expect(value).toBeLessThanOrEqual(4.5);

  // toBe and toEqual are equivalent for numbers
  expect(value).toBe(4);
  expect(value).toEqual(4);
});

For floating point equality, use toBeCloseTo instead of toEqual, because you don't want a test to depend on a tiny rounding error.

test('adding floating point numbers', () => {
  const value = 0.1 + 0.2;
  //expect(value).toBe(0.3);           This won't work because of rounding error
  expect(value).toBeCloseTo(0.3); // This works.
});

Şiruri de caractere

You can check strings against regular expressions with toMatch:

test('there is no I in team', () => {
  expect('team').not.toMatch(/I/);
});

test('but there is a "stop" in Christoph', () => {
  expect('Christoph').toMatch(/stop/);
});

Arrays and iterables

You can check if an array or iterable contains a particular item using toContain:

const shoppingList = [
  'diapers',
  'kleenex',
  'trash bags',
  'paper towels',
  'milk',
];

test('the shopping list has milk on it', () => {
  expect(shoppingList).toContain('milk');
  expect(new Set(shoppingList)).toContain('milk');
});

Excepţii

If you want to test whether a particular function throws an error when it's called, use toThrow.

function compileAndroidCode() {
  throw new Error('you are using the wrong JDK!');
}

test('compiling android goes as expected', () => {
  expect(() => compileAndroidCode()).toThrow();
  expect(() => compileAndroidCode()).toThrow(Error);

  // You can also use a string that must be contained in the error message or a regexp
  expect(() => compileAndroidCode()).toThrow('you are using the wrong JDK');
  expect(() => compileAndroidCode()).toThrow(/JDK/);

  // Or you can match an exact error message using a regexp like below
  expect(() => compileAndroidCode()).toThrow(/^you are using the wrong JDK$/); // Test fails
  expect(() => compileAndroidCode()).toThrow(/^you are using the wrong JDK!$/); // Test pass
});

tip

The function that throws an exception needs to be invoked within a wrapping function otherwise the toThrow assertion will fail.

Şi mai mult

This is just a taste. For a complete list of matchers, check out the reference docs.

Once you've learned about the matchers that are available, a good next step is to check out how Jest lets you test asynchronous code.