jest/valid-expect-in-promise

Require a promise chain that contains expect to be awaited or returned from the test

A callback passed to .then(), .catch() or .finally() runs later. If the test doesn't await or return the promise, Jest marks the test as passed before the expect in the callback runs, and a failed assertion doesn't fail the test.

Configure#

Off by default. To turn it on:

bunfig.toml
[lint.rules]
"jest/valid-expect-in-promise" = "error" # or "warn"

Examples#

example.ts1 problem
import { expect, test } from "@jest/globals";

test("loads the user", () => {
  loadUser(1).then((user) => {
    expect(user.name).toBe("Ada");
  });
});

You also need to await or return a promise that's kept in a variable:

example.ts1 problem
import { expect, test } from "@jest/globals";

test("loads the user", () => {
  const check = loadUser(1).then((user) => {
    expect(user.name).toBe("Ada");
  });
});

Code after the test's return never runs:

example.ts1 problem
import { expect, test } from "@jest/globals";

test("loads both users", () => {
  return loadUser(1).then((user) => {
    expect(user.name).toBe("Ada");
  });
  loadUser(2).then((user) => {
    expect(user.name).toBe("Grace");
  });
});
example.tsNo problems
import { expect, test } from "@jest/globals";

test("loads the user", () => {
  return loadUser(1).then((user) => {
    expect(user.name).toBe("Ada");
  });
});

test("loads the admin", async () => {
  await loadUser(2).then((user) => {
    expect(user.role).toBe("admin");
  });
});

test("loads the guest", async () => {
  const user = await loadUser(3);
  expect(user.role).toBe("guest");
});

You can await several promises together:

example.tsNo problems
import { expect, test } from "@jest/globals";

test("loads both users", async () => {
  const first = loadUser(1).then((user) => {
    expect(user.name).toBe("Ada");
  });
  const second = loadUser(2).then((user) => {
    expect(user.name).toBe("Grace");
  });
  await Promise.all([first, second]);
});

A test with a parameter isn't checked, because calling done is another way to make Jest wait:

example.tsNo problems
import { expect, test } from "@jest/globals";

test("loads the user", (done) => {
  loadUser(1).then((user) => {
    expect(user.name).toBe("Ada");
    done();
  });
});