Friday finking: TDD and EAFP

[Peter J. Holzer]

On 2019-11-04 07:41:32 +1300, DL Neil via Python-list wrote:
> On 3/11/19 6:30 AM, Bev In TX wrote:
> > > On Nov 1, 2019, at 12:40 AM, DL Neil via Python-list
> > > <python-list at python.org <mailto:python-list at python.org>> wrote:
> > > 
> > > Is the practice of TDD fundamentally, if not philosophically,
> > > somewhat contrary to Python's EAFP approach?
> 
> > I’m not an expert on either TDD or Python, but as no one else has
> > responded, I’ll put in my 2 cents worth...
> > You are mixing paradigms.  TDD is about testing code, regardless of the
> > style in which it was written.
> 
> Agreed: (in theory) TDD is independent of language or style. However, I'm
> wondering if (in practice) it creates a mode of thinking that pushes one
> into an EAFP way of thinking?

This is exactly the opposite of what you proposed in your first mail,
and I think it is closer to the truth:

TDD does in my opinion encourage EAFP thinking. 

The TDD is usually:

    1 Write a test
    2 Write the minimal amount of code that makes the test pass
    3 If you think you have covered the whole spec, stop, else repeat
      from 1

This is often (e.g. in [1]) exaggerated for pedagogic and humoristic
reasons. For example, your first test for a sqrt function might be 
    assert(sqrt(4) == 2)
and then of course the minimal implementation is
    def sqrt(x):
        return 2

Which just means that we don't have enough test cases yet. But the point
is that a test suite can only check a finite (and usually rather small)
number of cases, while most interesting programs accept a very large (if
not really infinite) number of inputs, so the test suite will always be
incomplete. At some point you will have to decide thet the test suite is
good enough and ship the code - and hope that the customer will forgive
you if you have (inevitably) forgotten an important case.

There is very little emphasis in TDD on verifying that the code is
correct - only that it passes the tests.

        hp

[1] Harry J.W. Percival, Test-Driven Development with Python, O'Reilly,
    2017

-- 
   _  | Peter J. Holzer    | Story must make more sense than reality.
|_|_) |                    |
| |   | hjp at hjp.at         |    -- Charles Stross, "Creative writing
__/   | http://www.hjp.at/ |       challenge!"
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