prefer-expect-assertions.md

Suggest using expect.assertions() OR expect.hasAssertions() (prefer-expect-assertions)

Ensure every test to have either expect.assertions(<number of assertions>) OR expect.hasAssertions() as its first expression.

Rule details

This rule triggers a warning if,

• expect.assertions(<number of assertions>) OR expect.hasAssertions() is not present as first statement in a test, e.g.:

test('my test', () => {
  expect(someThing()).toEqual('foo');
});

• expect.assertions(<number of assertions>) is the first statement in a test where argument passed to expect.assertions(<number of assertions>) is not a valid number, e.g.:

test('my test', () => {
  expect.assertions('1');
  expect(someThing()).toEqual('foo');
});

Default configuration

The following patterns are considered warnings:

test('my test', () => {
  expect.assertions('1');
  expect(someThing()).toEqual('foo');
});

test('my test', () => {
  expect(someThing()).toEqual('foo');
});

The following patterns would not be considered warnings:

test('my test', () => {
  expect.assertions(1);
  expect(someThing()).toEqual('foo');
});

test('my test', () => {
  expect.hasAssertions();
  expect(someThing()).toEqual('foo');
});

Options

onlyFunctionsWithAsyncKeyword

When true, this rule will only warn for tests that use the async keyword.

{
  "rules": {
    "jest/prefer-expect-assertions": [
      "warn",
      { "onlyFunctionsWithAsyncKeyword": true }
    ]
  }
}

When onlyFunctionsWithAsyncKeyword option is set to true, the following pattern would be a warning:

test('my test', async () => {
  const result = await someAsyncFunc();
  expect(result).toBe('foo');
});

While the following patterns would not be considered warnings:

test('my test', () => {
  const result = someFunction();
  expect(result).toBe('foo');
});

test('my test', async () => {
  expect.assertions(1);
  const result = await someAsyncFunc();
  expect(result).toBe('foo');
});