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Globals

In your test files, Jest puts each of these methods and objects into the global environment. You don't have to require or import anything to use them. However, if you prefer explicit imports, you can do import {describe, expect, test} from '@jest/globals'.

Métodos

Referencia

después de todo (fn, tiempo)

Runs a function after all the tests in this file have completed. If the function returns a promise or is a generator, Jest waits for that promise to resolve before continuing.

Optionally, you can provide a timeout (in milliseconds) for specifying how long to wait before aborting. Note: The default timeout is 5 seconds.

Esto es frecuentemente útil para restablecer el estado global compartido entre pruebas.

Por ejemplo:

const globalDatabase = makeGlobalDatabase();

function cleanUpDatabase(db) {
  db.cleanUp();
}

afterAll(() => {
  cleanUpDatabase(globalDatabase);
});

test('can find things', () => {
  return globalDatabase.find('thing', {}, results => {
    expect(results.length).toBeGreaterThan(0);
  });
});

test('can insert a thing', () => {
  return globalDatabase.insert('thing', makeThing(), response => {
    expect(response.success).toBeTruthy();
  });
});

La función afterAll garantiza que el método cleanUpDatabase sea llamado una vez terminada la ejecución de pruebas.

Si afterAll es llamado dentro de un bloque describe, este se ejecutará al final de la ejecución del bloque describe.

Si se desea ejecutar algún tipo de limpieza o restablecimiento después de cada prueba en lugar de al final de todas las pruebas, se puede utilizar afterEach.

afterEach(fn, tiempo)

Runs a function after each one of the tests in this file completes. If the function returns a promise or is a generator, Jest waits for that promise to resolve before continuing.

Optionally, you can provide a timeout (in milliseconds) for specifying how long to wait before aborting. Note: The default timeout is 5 seconds.

Esto es frecuentemente útil para restablecer algún estado temporal que sea creado por cada prueba.

Por ejemplo:

const globalDatabase = makeGlobalDatabase();

function cleanUpDatabase(db) {
  db.cleanUp();
}

afterEach(() => {
  cleanUpDatabase(globalDatabase);
});

test('can find things', () => {
  return globalDatabase.find('thing', {}, results => {
    expect(results.length).toBeGreaterThan(0);
  });
});

test('can insert a thing', () => {
  return globalDatabase.insert('thing', makeThing(), response => {
    expect(response.success).toBeTruthy();
  });
});

La función afterAll garantiza que el método cleanUpDatabase sea llamado una vez terminada cada prueba.

Si afterAll es llamado dentro de un bloque describe, este se ejecutará al final de la ejecución de cada prueba en el bloque describe.

Si se desea ejecutar algún tipo de limpieza o restablecimiento una sola vez por todas las pruebas, se puede utilizar afterAll.

beforeAll(fn, tiempo)

Runs a function before any of the tests in this file run. If the function returns a promise or is a generator, Jest waits for that promise to resolve before running tests.

Optionally, you can provide a timeout (in milliseconds) for specifying how long to wait before aborting. Note: The default timeout is 5 seconds.

Esto es frecuentemente útil para establecer algún estado global a ser ocupado por varias pruebas.

Por ejemplo:

const globalDatabase = makeGlobalDatabase();

beforeAll(() => {
  // Clears the database and adds some testing data.
  // Jest will wait for this promise to resolve before running tests.
  return globalDatabase.clear().then(() => {
    return globalDatabase.insert({testData: 'foo'});
  });
});

// Since we only set up the database once in this example, it's important
// that our tests don't modify it.
test('can find things', () => {
  return globalDatabase.find('thing', {}, results => {
    expect(results.length).toBeGreaterThan(0);
  });
});

Aquí el bloque beforeAll garantiza que la base de datos sea configurada antes de que se ejecuten las pruebas. If setup was synchronous, you could do this without beforeAll. La clave es que Jest espera a una promise para resolver, de modo que también se puede tener configuración inicial setup asincrona.

Si el bloque beforeAll se encuentra dentro de un bloque describe, esté se ejecutará al principio del bloque describe.

Si se desea ejecutar código antes de cada prueba en lugar de antes de todas las pruebas, se puede usar beforeEach.

beforeEach(fn, tiempo)

Runs a function before each of the tests in this file runs. If the function returns a promise or is a generator, Jest waits for that promise to resolve before running the test.

Optionally, you can provide a timeout (in milliseconds) for specifying how long to wait before aborting. Note: The default timeout is 5 seconds.

Esto es frecuentemente útil para restablecer algún estado global a ser ocupado por varias pruebas.

Por ejemplo:

const globalDatabase = makeGlobalDatabase();

beforeEach(() => {
  // Clears the database and adds some testing data.
  // Jest will wait for this promise to resolve before running tests.
  return globalDatabase.clear().then(() => {
    return globalDatabase.insert({testData: 'foo'});
  });
});

test('can find things', () => {
  return globalDatabase.find('thing', {}, results => {
    expect(results.length).toBeGreaterThan(0);
  });
});

test('can insert a thing', () => {
  return globalDatabase.insert('thing', makeThing(), response => {
    expect(response.success).toBeTruthy();
  });
});

Aquí el bloque beforeAll garantiza que la base de datos se restablezca antes de cada prueba.

Si el bloque beforeAll se encuentra dentro de un bloque describe, esté se ejecutará una vez antes de cada prueba en el bloque describe.

Si se desea ejecutar código de configuración inicial, una sola vez antes de cualquier prueba, usesé beforeAll.

describe(name, fn)

describe(name, fn) creates a block that groups together several related tests. Por ejemplo, si se tiene una objeto myBeverage que representa una bebida que debe ser deliciosa pero no agria, se podría probar con:

const myBeverage = {
  delicious: true,
  sour: false,
};

describe('my beverage', () => {
  test('is delicious', () => {
    expect(myBeverage.delicious).toBeTruthy();
  });

  test('is not sour', () => {
    expect(myBeverage.sour).toBeFalsy();
  });
});

This isn't required - you can write the test blocks directly at the top level. But this can be handy if you prefer your tests to be organized into groups.

También se pueden anidar bloques describe si se tiene una jerarquía de pruebas:

const cadenaBinariaANumero = cadenaBinaria => {
  if (!/^[01]+$/.test(cadenaBinaria)) {
    throw new CustomError('No es un número binario.');
  }

  return parseInt(cadenaBinaria, 2);
};

describe('cadenaBinariaANumero', () => {
  describe('dada una cadena binaria invalida', () => {
    test('compuesta de no-números arroja un CustomError', () => {
      expect(() => cadenaBinariaANumero('abc')).toThrowError(CustomError);
    });

    test('con espacios en blanco extra arroja un CustomError', () => {
      expect(() => cadenaBinariaANumero('  100')).toThrowError(CustomError);
    });
  });

  describe('dada una cadena binaria valida', () => {
    test('regresa el número correcto', () => {
      expect(cadenaBinariaANumero('100')).toBe(4);
    });
  });
});

describe.each(table)(name, fn, timeout)

Use describe.each if you keep duplicating the same test suites with different data. describe.each allows you to write the test suite once and pass data in.

describe.each is available with two APIs:

1. describe.each(table)(name, fn, timeout)

  • table: Array of Arrays with the arguments that are passed into the fn for each row.
    • Note If you pass in a 1D array of primitives, internally it will be mapped to a table i.e. [1, 2, 3] -> [[1], [2], [3]]
  • name: String the title of the test suite.
    • Generate unique test titles by positionally injecting parameters with printf formatting:
      • %p - pretty-format.
      • %s- String.
      • %d- Number.
      • %i - Integer.
      • %f - Floating point value.
      • %j - JSON.
      • %o - Object.
      • %# - Index of the test case.
      • %% - single percent sign ('%'). This does not consume an argument.
  • fn: Function the suite of tests to be ran, this is the function that will receive the parameters in each row as function arguments.
  • Optionally, you can provide a timeout (in milliseconds) for specifying how long to wait for each row before aborting. Note: The default timeout is 5 seconds.

Ejemplo:

describe.each([
  [1, 1, 2],
  [1, 2, 3],
  [2, 1, 3],
])('.add(%i, %i)', (a, b, expected) => {
  test(`returns ${expected}`, () => {
    expect(a + b).toBe(expected);
  });

  test(`returned value not be greater than ${expected}`, () => {
    expect(a + b).not.toBeGreaterThan(expected);
  });

  test(`returned value not be less than ${expected}`, () => {
    expect(a + b).not.toBeLessThan(expected);
  });
});

2. describe.each`table`(name, fn, timeout)

  • table: Tagged Template Literal
    • First row of variable name column headings separated with |
    • One or more subsequent rows of data supplied as template literal expressions using ${value} syntax.
  • name: String the title of the test suite, use $variable to inject test data into the suite title from the tagged template expressions.
    • To inject nested object values use you can supply a keyPath i.e. $variable.path.to.value
  • fn: Function the suite of tests to be ran, this is the function that will receive the test data object.
  • Optionally, you can provide a timeout (in milliseconds) for specifying how long to wait for each row before aborting. Note: The default timeout is 5 seconds.

Ejemplo:

describe.each`
  a    | b    | expected
  ${1} | ${1} | ${2}
  ${1} | ${2} | ${3}
  ${2} | ${1} | ${3}
`('$a + $b', ({a, b, expected}) => {
  test(`returns ${expected}`, () => {
    expect(a + b).toBe(expected);
  });

  test(`returned value not be greater than ${expected}`, () => {
    expect(a + b).not.toBeGreaterThan(expected);
  });

  test(`returned value not be less than ${expected}`, () => {
    expect(a + b).not.toBeLessThan(expected);
  });
});

describe.only(name, fn)

Se puede encontrar también debajo del alias: fdescribe(name, fn)

Se puede utilizar describe.only si se desea ejecutar solo ún bloque describe:

describe.only('my beverage', () => {
  test('is delicious', () => {
    expect(myBeverage.delicious).toBeTruthy();
  });

  test('is not sour', () => {
    expect(myBeverage.sour).toBeFalsy();
  });
});

describe('my other beverage', () => {
  // ... will be skipped
});

describe.only.each(table)(name, fn)

Also under the aliases: fdescribe.each(table)(name, fn) and fdescribe.each`table`(name, fn)

Use describe.only.each if you want to only run specific tests suites of data driven tests.

describe.only.each is available with two APIs:

describe.only.each(table)(name, fn)

describe.only.each([
  [1, 1, 2],
  [1, 2, 3],
  [2, 1, 3],
])('.add(%i, %i)', (a, b, expected) => {
  test(`returns ${expected}`, () => {
    expect(a + b).toBe(expected);
  });
});

test('will not be ran', () => {
  expect(1 / 0).toBe(Infinity);
});

describe.only.each`table`(name, fn)

describe.only.each`
  a    | b    | expected
  ${1} | ${1} | ${2}
  ${1} | ${2} | ${3}
  ${2} | ${1} | ${3}
`('returns $expected when $a is added $b', ({a, b, expected}) => {
  test('passes', () => {
    expect(a + b).toBe(expected);
  });
});

test('will not be ran', () => {
  expect(1 / 0).toBe(Infinity);
});

describe.skip(name, fn)

Se puede encontrar también debajo del alias: xdescribe(name, fn)

Se puede utilizar describe.skip si se desea omitirun bloque describe en particular:

describe('my beverage', () => {
  test('is delicious', () => {
    expect(myBeverage.delicious).toBeTruthy();
  });

  test('is not sour', () => {
    expect(myBeverage.sour).toBeFalsy();
  });
});

describe.skip('my other beverage', () => {
  // ... will be skipped
});

Using describe.skip is often a cleaner alternative to temporarily commenting out a chunk of tests.

describe.skip.each(table)(name, fn)

Also under the aliases: xdescribe.each(table)(name, fn) and xdescribe.each`table`(name, fn)

Use describe.skip.each if you want to stop running a suite of data driven tests.

describe.skip.each is available with two APIs:

describe.skip.each(table)(name, fn)

describe.skip.each([
  [1, 1, 2],
  [1, 2, 3],
  [2, 1, 3],
])('.add(%i, %i)', (a, b, expected) => {
  test(`returns ${expected}`, () => {
    expect(a + b).toBe(expected); // will not be ran
  });
});

test('will be ran', () => {
  expect(1 / 0).toBe(Infinity);
});

describe.skip.each`table`(name, fn)

describe.skip.each`
  a    | b    | expected
  ${1} | ${1} | ${2}
  ${1} | ${2} | ${3}
  ${2} | ${1} | ${3}
`('returns $expected when $a is added $b', ({a, b, expected}) => {
  test('will not be ran', () => {
    expect(a + b).toBe(expected); // will not be ran
  });
});

test('will be ran', () => {
  expect(1 / 0).toBe(Infinity);
});

prueba(nombre, fn, tiempo)

También con el alias: it(name, fn, tiempo)

All you need in a test file is the test method which runs a test. For example, let's say there's a function inchesOfRain() that should be zero. Your whole test could be:

test('did not rain', () => {
  expect(inchesOfRain()).toBe(0);
});

El primer argumento es el nombre de la prueba, el segundo argumento es una función con el codigo de expectativas a ser probadas. The third argument (optional) is timeout (in milliseconds) for specifying how long to wait before aborting. Note: The default timeout is 5 seconds.

Note: If a promise is returned from test, Jest will wait for the promise to resolve before letting the test complete. Jest will also wait if you provide an argument to the test function, usually called done. This could be handy when you want to test callbacks. See how to test async code here.

For example, let's say fetchBeverageList() returns a promise that is supposed to resolve to a list that has lemon in it. Podemos probarlo con:

test('has lemon in it', () => {
  return fetchBeverageList().then(list => {
    expect(list).toContain('lemon');
  });
});

Aunque la llamada al test terminará inmediatamente, la prueba no será completada hasta que resuelva el promise.

test.each(table)(name, fn, timeout)

Also under the alias: it.each(table)(name, fn) and it.each`table`(name, fn)

Use test.each if you keep duplicating the same test with different data. test.each allows you to write the test once and pass data in.

test.each is available with two APIs:

1. test.each(table)(name, fn, timeout)

  • table: Array of Arrays with the arguments that are passed into the test fn for each row.
    • Note If you pass in a 1D array of primitives, internally it will be mapped to a table i.e. [1, 2, 3] -> [[1], [2], [3]]
  • name: String the title of the test block.
    • Generate unique test titles by positionally injecting parameters with printf formatting:
      • %p - pretty-format.
      • %s- String.
      • %d- Number.
      • %i - Integer.
      • %f - Floating point value.
      • %j - JSON.
      • %o - Object.
      • %# - Index of the test case.
      • %% - single percent sign ('%'). This does not consume an argument.
  • fn: Function the test to be ran, this is the function that will receive the parameters in each row as function arguments.
  • Optionally, you can provide a timeout (in milliseconds) for specifying how long to wait for each row before aborting. Note: The default timeout is 5 seconds.

Ejemplo:

test.each([
  [1, 1, 2],
  [1, 2, 3],
  [2, 1, 3],
])('.add(%i, %i)', (a, b, expected) => {
  expect(a + b).toBe(expected);
});

2. test.each`table`(name, fn, timeout)

  • table: Tagged Template Literal
    • First row of variable name column headings separated with |
    • One or more subsequent rows of data supplied as template literal expressions using ${value} syntax.
  • name: String the title of the test, use $variable to inject test data into the test title from the tagged template expressions.
    • To inject nested object values use you can supply a keyPath i.e. $variable.path.to.value
  • fn: Function the test to be ran, this is the function that will receive the test data object.
  • Optionally, you can provide a timeout (in milliseconds) for specifying how long to wait for each row before aborting. Note: The default timeout is 5 seconds.

Ejemplo:

test.each`
  a    | b    | expected
  ${1} | ${1} | ${2}
  ${1} | ${2} | ${3}
  ${2} | ${1} | ${3}
`('returns $expected when $a is added $b', ({a, b, expected}) => {
  expect(a + b).toBe(expected);
});

prueba.solo(name, fn, tiempo)

Also under the aliases: it.only(name, fn, timeout), and fit(name, fn, timeout)

When you are debugging a large test file, you will often only want to run a subset of tests. You can use .only to specify which tests are the only ones you want to run in that test file.

Optionally, you can provide a timeout (in milliseconds) for specifying how long to wait before aborting. Note: The default timeout is 5 seconds.

Por ejemplo, digamos que se tuviera estas pruebas:

test.only('it is raining', () => {
  expect(inchesOfRain()).toBeGreaterThan(0);
});

test('it is not snowing', () => {
  expect(inchesOfSnow()).toBe(0);
});

Only the "it is raining" test will run in that test file, since it is run with test.only.

Usually you wouldn't check code using test.only into source control - you would use it for debugging, and remove it once you have fixed the broken tests.

test.only.each(table)(name, fn)

Also under the aliases: it.only.each(table)(name, fn), fit.each(table)(name, fn), it.only.each`table`(name, fn) and fit.each`table`(name, fn)

Use test.only.each if you want to only run specific tests with different test data.

test.only.each is available with two APIs:

test.only.each(table)(name, fn)

test.only.each([
  [1, 1, 2],
  [1, 2, 3],
  [2, 1, 3],
])('.add(%i, %i)', (a, b, expected) => {
  expect(a + b).toBe(expected);
});

test('will not be ran', () => {
  expect(1 / 0).toBe(Infinity);
});

test.only.each`table`(name, fn)

test.only.each`
  a    | b    | expected
  ${1} | ${1} | ${2}
  ${1} | ${2} | ${3}
  ${2} | ${1} | ${3}
`('returns $expected when $a is added $b', ({a, b, expected}) => {
  expect(a + b).toBe(expected);
});

test('will not be ran', () => {
  expect(1 / 0).toBe(Infinity);
});

test.skip(name, fn)

Also under the aliases: it.skip(name, fn), xit(name, fn), and xtest(name, fn)

Cuando se trabaja en una gran base de código, es frecuente encontrar alguna prueba que falla de manera temporal. If you want to skip running this test, but you don't want to delete this code, you can use test.skip to specify some tests to skip.

Por ejemplo, digamos que se tuviera estas pruebas:

test('it is raining', () => {
  expect(inchesOfRain()).toBeGreaterThan(0);
});

test.skip('it is not snowing', () => {
  expect(inchesOfSnow()).toBe(0);
});

Sólo se ejecutaría la prueba "it is raning", pues se agregó test.skip a la otra prueba.

You could comment the test out, but it's often a bit nicer to use test.skip because it will maintain indentation and syntax highlighting.

test.skip.each(table)(name, fn)

Also under the aliases: it.skip.each(table)(name, fn), xit.each(table)(name, fn), xtest.each(table)(name, fn), it.skip.each`table`(name, fn), xit.each`table`(name, fn) and xtest.each`table`(name, fn)

Use test.skip.each if you want to stop running a collection of data driven tests.

test.skip.each is available with two APIs:

test.skip.each(table)(name, fn)

test.skip.each([
  [1, 1, 2],
  [1, 2, 3],
  [2, 1, 3],
])('.add(%i, %i)', (a, b, expected) => {
  expect(a + b).toBe(expected); // will not be ran
});

test('will be ran', () => {
  expect(1 / 0).toBe(Infinity);
});

test.skip.each`table`(name, fn)

test.skip.each`
  a    | b    | expected
  ${1} | ${1} | ${2}
  ${1} | ${2} | ${3}
  ${2} | ${1} | ${3}
`('returns $expected when $a is added $b', ({a, b, expected}) => {
  expect(a + b).toBe(expected); // will not be ran
});

test('will be ran', () => {
  expect(1 / 0).toBe(Infinity);
});

test.todo(name)

Also under the alias: it.todo(name)

Use test.todo when you are planning on writing tests. These tests will be highlighted in the summary output at the end so you know how many tests you still need todo.

Note: If you supply a test callback function then the test.todo will throw an error. If you have already implemented the test and it is broken and you do not want it to run, then use test.skip instead.

API

  • name: String the title of the test plan.

Ejemplo:

const add = (a, b) => a + b;

test.todo('add should be associative');
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