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no-tautological-length-assertions

Disallow length assertions that only prove length is non-negative.

Rule detailsโ€‹

Array and string lengths are already non-negative. Assertions such as expect(items.length).toBeGreaterThanOrEqual(0) look like coverage, but they do not prove that the collection has the expected number of items or contents. They also keep passing when the implementation returns an empty collection.

Incorrectโ€‹

it("returns items", () => {
    expect(loadItems().length).toBeGreaterThanOrEqual(0);
});
it("returns items", () => {
    expect(loadItems().length).not.toBeLessThan(0);
});

Correctโ€‹

it("returns two items", () => {
    expect(loadItems()).toHaveLength(2);
});
it("returns at least one item", () => {
    expect(loadItems().length).toBeGreaterThan(0);
});

What this rule reportsโ€‹

This rule reports executable it(...) and test(...) callbacks with tautological lower-bound checks against .length:

  • expect(value.length).toBeGreaterThanOrEqual(0)
  • expect(value.length).toBeGreaterThan(-1)
  • expect(value.length).not.toBeLessThan(0)
  • expect(value.length).not.toBeLessThanOrEqual(-1)

The rule intentionally does not follow variables or fold arbitrary expressions. Computed thresholds remain valid because they usually encode a project-specific contract.

Optionsโ€‹

This rule has no options.

When not to use itโ€‹

Disable this rule for unusual tests that intentionally document JavaScript runtime invariants. Product tests should assert an exact length, a positive minimum, or expected contents.

Rule catalog ID: R019