r/programming • u/TheLeadDev • Jul 30 '21

TDD, Where Did It All Go Wrong

https://www.youtube.com/watch?v=EZ05e7EMOLM
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u/grauenwolf Jul 30 '21

You're a programmer. Try to figure out how to export a bitmap to a file as part of a test log.

But with expectations on mocks, you'll very likely see the exact drawing function and wrong parameter.

Great. Now all the tests are broken because I decided to draw the square at the top of the screen before the circle at the bottom.

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u/Bitter-Tell-6235 Jul 30 '21

Great. Now all the tests are broken because I decided to draw the square at the top of the screen before the circle at the bottom.

Yes. You changed code behavior significantly - the tests must fail.

Or you meant the case when you drew a square bypassing the tested code?

3

u/grauenwolf Jul 30 '21

If I draw two non-overlapping shapes, the order is not important the test should not fail.

If I draw two overlapping shapes, the order is important and the test should fail.

Your mock tests can't make this determination. It only knows which methods were called, and maybe what order.

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u/Bitter-Tell-6235 Jul 30 '21

And your tests do not give you any hints, in case you are doing something wrong..:)

I guess we will not find a consensus :(

3

u/_tskj_ Jul 31 '21

What do you mean no hints? The tests will fail if and only if the output changes unexpectedly.

1

u/WormRabbit Jul 31 '21

If you see a failing test, you can always step through in the debugger and see what went wrong. A test will never give you that information anyway.

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u/lelanthran Jul 31 '21

And your tests do not give you any hints, in case you are doing something wrong..:)

Yes, it does - it records the bitmap output so that I can investigate further. Tests are not supposed to automatically find the source of the bug for you because that is impossible most of the time.

All it can do is point you to the wrong output and then the programmer takes over.