tautological-assertion

An assertion compares a value with itself.

Group

Tests

Runs

On by default

Level

warning

Reads

Tests

Fix

None: what the test should expect is the author's choice

Defends

Fidelity: when the code is broken, the test fails.

Why

Both sides of the assertion are the same term, once each local the test assigns once is replaced by its value, so the assertion cannot fail. Ur does not yet know a value's type, so a test of a type's own ==, such as assert_eq!(x, x), is reported too; mark one written on purpose with ur-allow. A variable compared with itself by identity is left to vacuous-assertion.

The fix, as Ur suggests it: compare with a value stated independently of the code.

For agents

Compare the result of the code under test with a value stated independently of it, never with the same expression.

class Cart:
    def __init__(self, prices):
        self.prices = prices

    def total(self):
        return sum(self.prices)

from shop.cart import Cart


def test_total():
    cart = Cart([24, 8])
    expected = cart.total()
    assert cart.total() == expected

$ ur lint --rule tautological-assertion
warning[tautological-assertion]: both sides of `assert` in test `test_total` are the same value, so it cannot fail
  --> ./tests/test_cart.py:7:5 test `test_total`
  = hint: compare with a value stated independently of the code
  = see: Testing on the Toilet: Effective Testing, Google Testing Blog (2014-05-07), https://testing.googleblog.com/2014/05/testing-on-toilet-effective-testing.html
0 clone classes and 1 test finding in 2 files

Source

Testing on the Toilet: Effective Testing, Google Testing Blog (2014-05-07).