Local Variables as Accidental Breadcrumbs for Faster Debugging

Re:Local Variables as Accidental Breadcrumbs for Faster Debu... by aftbit on Thursday October 10, 2024 @06:14PM (#41804112)

Is there a reason you need specialized assertions over something like Python's generic assert?

    >>> big = 2; small = 3
    >>> assert big >= small, "big is smaller than small"
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    AssertionError: big is smaller than small

In pytest, assertions are rewritten[1] to return something more useful like:

        def test():
            big = 2
            small = 3
    >       assert big > small
    E       assert 2 > 3
    
    test/test_dumb.py:4: AssertionError
    ========== short test summary info ==========
    FAILED test/test_dumb.py::test - assert 2 > 3

1: https://github.com/pytest-dev/pytest/blob/f373974707f57a0b28...

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Re:Local Variables as Accidental Breadcrumbs for Faster Debu... by Arnavion on Thursday October 10, 2024 @06:31PM (#41804234)

Rust has a generic assert too `assert!(foo >= bar);`. I assume (haven't used the crate myself) the advantage of `assertable::assert_ge!(foo, bar)` is that it prints the values of foo and bar in the assert message. The `assert_eq!(foo, bar)` and `assert_ne!(foo, bar)` macros provided by Rust libstd also do this. But the generic `assert!()` just sees the boolean result of its expression and only prints that in its message.

The values of the variables can be included in the generic macro's message via a custom message format, like `assert!(foo >= bar, "foo = {foo}, bar = {bar}");` but having the macro do it by default is convenient. There is an old discussion to have the `assert!()` macro parse its expression to figure out what variables are there and print them out by default, but it's still WIP. ( https://github.com/rust-lang/rfcs/blob/master/text/2011-gene... https://github.com/rust-lang/rust/issues/44838 )

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Re:Local Variables as Accidental Breadcrumbs for Faster Debu... by o11c on Thursday October 10, 2024 @07:00PM (#41804433)

What's more, pytest errs on the side of "just capture more" and In my experience it's quite useful:

  ============================= test session starts ==============================
  platform linux -- Python 3.11.2, pytest-7.2.1, pluggy-1.0.0+repack
  rootdir: /tmp/dl/py
  collected 1 item                                                               
  
  test_bigsmall.py F                                                       [100%]
  
  =================================== FAILURES ===================================
  ________________________________ test_something ________________________________
  
      def test_something():
  >       assert get_big_number() > get_small_number()
  E       assert 0 > 1
  E        +  where 0 = get_big_number()
  E        +  and   1 = get_small_number()
  
  test_bigsmall.py:8: AssertionError
  =========================== short test summary info ============================
  FAILED test_bigsmall.py::test_something - assert 0 > 1
  ============================== 1 failed in 0.06s ===============================

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