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no-weak-existence-assertions

Disallow broad existence assertions in executable tests.

Rule detailsโ€‹

Existence checks prove only that a value is not one narrow absence case. They do not verify the expected boolean, object shape, collection length, status code, or domain state. A test using toBeDefined() or not.toBeNull() can keep passing after the implementation returns the wrong object, an empty collection, false, or another unintended value.

Incorrectโ€‹

it("returns a user", () => {
    expect(loadUser("abc")).toBeDefined();
});
it("returns a user", () => {
    expect(loadUser("abc")).not.toBeNull();
});

Correctโ€‹

it("returns a user", () => {
    expect(loadUser("abc")).toEqual({
        enabled: true,
        id: "abc",
    });
});
it("omits missing users", () => {
    expect(loadUser("missing")).toBeUndefined();
});

What this rule reportsโ€‹

This rule reports executable it(...) and test(...) callbacks that use broad existence assertions:

  • expect(value).toBeDefined()
  • expect(value).not.toBeNull()
  • expect(value).not.toBeUndefined()
  • promise-modified forms such as await expect(value).resolves.not.toBeUndefined()

Positive absence assertions such as toBeNull() and toBeUndefined() remain valid because they verify a concrete absence state.

Optionsโ€‹

This rule has no options.

When not to use itโ€‹

Disable this rule for smoke tests whose only contract is that a framework hook returns some value. For most product tests, prefer exact booleans, object shapes, collection lengths, or explicit absence assertions.

Rule catalog ID: R016