vitest/valid-expect-in-promise

A callback passed to .then(), .catch() or .finally() runs later. If the test doesn't await or return the promise, Vitest 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:

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

Examples

Reported:

import { expect, test } from "vitest";

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

A promise kept in a variable must be awaited or returned too:

import { expect, test } from "vitest";

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

Code after the test's return never runs:

import { expect, test } from "vitest";

test("loads both users", () => {
  return loadUser(1).then((user) => {
    expect(user.name).toBe("Ada");
  });
  loadUser(2).then((user) => {
    expect(user.name).toBe("Grace");
  });
});

Not reported:

import { expect, test } from "vitest";

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:

import { expect, test } from "vitest";

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. This test takes the test context, so the rule misses the promise that nobody waits for:

import { test } from "vitest";

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