jest/expect-expect

Require every test to make at least one assertion

A test with no assertion passes as long as the code doesn't throw, whether the result is right or wrong. Usually someone forgot the expect, or lost it while changing the test.

test.todo isn't checked. test.skip is.

Configure#

Off by default. To turn it on:

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

Every option, set to its default:

bunfig.toml
[lint.rules]
"jest/expect-expect" = ["error", {
  assertFunctionNames = ["expect"],
  additionalTestBlockFunctions = [], # list of strings
}]

Examples#

example.ts2 problems
import { test } from "@jest/globals";

test("parses the port", () => {
  parseConfig("port = 3000");
});

test.skip("parses the host", () => {
  parseConfig("host = localhost");
});
example.tsNo problems
import { expect, test } from "@jest/globals";

test("parses the port", () => {
  expect(parseConfig("port = 3000")).toEqual({ port: 3000 });
});

test.todo("parses the host");

Options#

OptionDefaultWhat it does
assertFunctionNames["expect"]The functions that count as an assertion. Your list replaces the default, so keep "expect" in it.
additionalTestBlockFunctions[]Other Jest functions to check like test, such as "afterEach".

assertFunctionNames#

The rule doesn't look inside the helpers that a test calls. This test is reported even though checkUser calls expect:

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

function checkUser(user) {
  expect(user.id).toBeGreaterThan(0);
}

test("creates a user", () => {
  checkUser(createUser());
});

Add the helper's name and the report goes away:

bunfig.toml
[lint.rules]
"jest/expect-expect" = ["error", {
  assertFunctionNames = ["expect", "checkUser"],
}]
example.tswith { "assertFunctionNames": ["expect", "checkUser"] }No problems
import { expect, test } from "@jest/globals";

function checkUser(user) {
  expect(user.id).toBeGreaterThan(0);
}

test("creates a user", () => {
  checkUser(createUser());
});

A name can be a chain, such as request.get.expect. * matches any letters and digits in one part of the chain, and ** matches one or more parts. Case is ignored.

With "request.**.expect" in the list, this isn't reported:

example.tswith { "assertFunctionNames": ["expect", "request.**.expect"] }No problems
import { test } from "@jest/globals";

test("is healthy", async () => {
  await request(app).get("/health").expect(200);
});

additionalTestBlockFunctions#

This option only works for functions that come from Jest. With ["afterEach"], this is reported:

example.tswith { "additionalTestBlockFunctions": ["afterEach"] }1 problem
import { afterEach } from "@jest/globals";

afterEach(() => {
  closeDatabase();
});

Your own wrappers aren't checked, even if you list them. With ["testWithDatabase"], this isn't reported:

example.tswith { "additionalTestBlockFunctions": ["testWithDatabase"] }No problems
import { afterAll } from "@jest/globals";
import { closeDatabase, testWithDatabase } from "./helpers";

afterAll(closeDatabase);

testWithDatabase("saves the user", (db) => {
  db.save(createUser());
});