uninformative-assertion

An assertion is given only the result of a comparison.

Group

Tests

Runs

On by default

Level

note

Reads

Tests

Fix

None: the comparing assertion takes the two sides as separate arguments, which a rewrite of the call does not yet produce

Defends

Precision: when the test fails, its failure says where to look.

Why

The assertion receives true or false, so its failure can only say that it was false, where an assertion given both values would show what each one was. Only a comparison the framework has a comparing assertion for is reported, and the finding names it: assert!(a == b) is assert_eq!, but assert!(a < b) has no better spelling. pytest's assert rewrites the comparison, and a message that prints both values already shows them, so neither is reported.

The fix, as Ur suggests it: pass both values to the comparing assertion the finding names.

For agents

Pass the two values to an assertion that compares them, such as assert_eq! or assertEquals, rather than asserting that a comparison holds.

class Invoice:
    def __init__(self, subtotal):
        self.subtotal = subtotal

    def total(self, tax_rate):
        return round(self.subtotal * (1 + tax_rate), 2)

import unittest

from shop.invoice import Invoice


class InvoiceTest(unittest.TestCase):
    def test_adds_tax(self):
        invoice = Invoice(subtotal=80)
        self.assertTrue(invoice.total(tax_rate=0.25) == 100)

$ ur lint --rule uninformative-assertion
note[uninformative-assertion]: `assertTrue` is given the result of a comparison, so its failure cannot show the values compared; `assertEqual` would
  --> ./tests/test_invoice.py:9:9 test `test_adds_tax`
  = hint: pass both values to the comparing assertion the finding names
  = see: Test Failures Should Be Actionable, Google Testing Blog (2024-05-06), https://testing.googleblog.com/2024/05/test-failures-should-be-actionable.html
0 clone classes and 1 test finding in 2 files

Source

Test Failures Should Be Actionable, Google Testing Blog (2024-05-06).