Tests fail if there's _ (underscore) defined in the notebook

[sidujjain]

Is there a way to handle this?

Test:

from testbook import testbook

@testbook('nb.ipynb', execute=True)
def test_foo(tb):
    foo = tb.ref("foo")
    assert foo(2) == 3

Notebook:

_ = 20

def foo(x):
    return x + 1

Result:

    @testbook('nb.ipynb', execute=True)
    def test_foo(tb):
        foo = tb.ref("foo")
>       assert foo(2) == 3
E       AssertionError: assert 20 == 3
E        +  where 20 = <[TypeError('__repr__ returned non-string (type int)') raised in repr()] TestbookObjectReference object at 0x7ff04d735c90>(2)

tb.py:6: AssertionError
======================================================================== short test summary info ========================================================================
FAILED tb.py::test_foo - AssertionError: assert 20 == 3

[MSeal]

So I have a fix for the type error occurring when reporting the value of foo(2).

However the root problem is that testbook is using the _ variable to fetch the execution value of the last cell. In ipython this has special meaning:

In [1]: 1 + 1
Out[1]: 2

In [2]: _
Out[2]: 2

However when you do an underscore assignment like _ = 20 you permanently assign that variable to 20 causing all 'last-value' checks to say they got a value of 20.

In [1]: _ = 20

In [2]: 1 + 1
Out[2]: 2

In [3]: _
Out[3]: 20

Generally I would avoid doing _ assignments within a notebook, though I'll submit the patch here in a second to make it so the assertion at least reports the error accurately as 20 == 3 assertion failure.

[rohitsanj]

@sidujjain Thanks for reporting. Will look into this now.

@MSeal thanks for the change, I'll see if I can add a fix to the same PR.

[sidujjain]

Thanks for the quick response, @MSeal ! Using _ is a common pattern in python for unpacking tuples or in loops.

I wonder if there is a way to capture the output in a different way or to reset _ before running the Testbook tests.

[MSeal]

Yeah I know, though it's somewhat more of an ipython limitation: https://stackoverflow.com/questions/56734319/reset-underscore-variable-in-jupyter-notebook-powered-by-ipython-kernel. That link has some paths to fix the root issue. @rohitsanj we could see about forcing the result outcome each injection to see if we can auto-repair it?

[rohitsanj]

@sidujjain Please upgrade to testbook 0.2.6 and the issue should be fixed!

pip install -U testbook

[sidujjain]

Thanks for the quick fix @rohitsanj ! Works like a charm!