[hitchstory]

When I do TDD (virtually every time i write a line of code) each test scenario isnt just a way to verify that the code is working, it's also a specification - often for a previously unconsidered edge case.

Throwing away the test means throwing away that user story and the value that comes with it.

[youerbt]

I believe you (other than tests being specifications, they are examples at best). But that doesn't change the fact that TDD looks more adopted in untyped languages, and that deserves an explanation.

Mine is that a lot of potential errors (typos, type mismatches) don't need to be exercised by running code in typed language.

Yours is... well, you don't really address it.

[hitchstory]

>I believe you other than tests being specifications

If you're not, that suggests you're not doing them right which in turn suggests why you might have an issue with them...

[drdeca]

How would you make a test a specification?

I suppose you could do something like, enumerate every possible combination of inputs and check that some property holds for all of them. Or, maybe you could instead randomly select a number of combinations of inputs and check that a property holds for each of those random combinations, but that wouldn't be guaranteed to find the inputs for which the specification isn't satisfied.

I guess maybe if the test passed to the function to be tested, mock values, such that the function is effectively evaluated symbolically (where any branching that depends on the inputs to the function, would maybe have the mocked object specify what the result of the conditional should be, with different tests for different cases?) ?

Or.. Can you explain how you write tests such that they truly function as specifications?

[earth_walker]

Good question - and there's been lots of work on this area. See for example property testing and fuzz testing, which can do something similar to what your second paragraph suggests.

You should be able to find a property testing library in your favourite language such as Hypothesis (python), Quickcheck (Haskell), Fastcheck (JS/typescript), etc.

[hitchstory]

Jane logs in, enters her DOB which is 11/5/1998, does Y the result of which is Z.

Where X, Y and Z are very specific.

These example scenarios work well as a communication medium for discussing intended program behavior as well as translating well into tests.

>enumerate every possible combination

Whereas if you start doing this you will probably confuse your stakeholders.

Specific examples tend to make better specifications.

[drdeca]

A “specification” which is based on just “the desired behavior in a few specific examples” seems to allow undesired behavior without it being clear whether said behavior is allowed by the spec.

That to me doesn’t seem like what a “specification” is.

Now, maybe having good examples is more important for business use cases than having a specification.

But I generally wouldn’t call it one.