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no-identical-expected-actual

Disallow assertions that compare a value to itself.

Rule detailsโ€‹

Self-comparisons are tautologies. They can survive copy/paste mistakes and keep passing even when the code under test returns the wrong value. The assertion looks specific, but the expected value is not independent from the actual value.

Incorrectโ€‹

it("returns the saved user", () => {
    const user = saveUser({ id: "abc" });

    expect(user).toEqual(user);
});
it("returns the current state", () => {
    expect(store.state.current).toStrictEqual(store.state.current);
});

Correctโ€‹

it("returns the saved user", () => {
    expect(saveUser({ id: "abc" })).toEqual({
        id: "abc",
    });
});
it("returns the current state", () => {
    const expectedState = createExpectedState();

    expect(store.state.current).toStrictEqual(expectedState);
});

What this rule reportsโ€‹

This rule reports executable it(...) and test(...) callbacks where equality or shape matchers compare the assertion subject to the same source expression:

  • expect(value).toBe(value)
  • expect(value).toEqual(value)
  • expect(value).toStrictEqual(value)
  • expect(value).toMatchObject(value)

The check is intentionally syntax-level. Aliases such as const expected = value; expect(value).toEqual(expected) are not reported because proving alias identity would require type and control-flow analysis that is too noisy for this rule.

Optionsโ€‹

This rule has no options.

When not to use itโ€‹

This rule is intended for normal product tests. Disable it for unusual meta-tests that intentionally verify custom matcher behavior with tautological inputs.

Rule catalog ID: R017