Monday, May 19, 2014

Test First vs Test After

There has been a lot of talk lately about whether or not Test First is Dead.
This is a complicated and tangled issue, so I want to simplify many aspects of this debate in this blog post to focus on a single aspect of TDD: time.

So for this blog, let's ignore the distinction between unit, integration, acceptance tests. I'll lump them all together into a single box  - 'tests'.

Let's focus on the speed aspects of Test First vs Test After.

Test After

To start, we'll look at the time it takes to write code using test after.
I'm going to use a lean graph to help map the differences between 'actual work' and 'non-work'. I get paid to write code, not tests, so I'll map code to work and tests to 'non-work'.
In this example, it took me 60 minutes to code a feature. Then more time to write the tests for that feature.

Now for the key question:

"Is it faster to not write the tests?"

In other words, which is true:
 a)  60  < 60 + X
 b)  60  > 60 + X

This is obviously  a)  60  < 60 + X  regardless of how long or quickly you can write the tests.
This doesn't mean that in the long term it isn't faster to write tests, but it does mean in the short term, if you write tests after, it will always take you longer.

so what about...

Test First

When you have a test before you start it can make it easier for you to write the code. This is because the Tests can aid with Specification & Feedback of the task at hand. This saves some time. Again, we'll assume for this example that it saves me 30 minutes while writing the code.

Now for the key question:

"Is it faster to not write the tests?"

In other words, which is true:
 a)  60  < 30 + X
 b)  60  > 30 + X

This is a more difficult question. It depends on how long it took to write the tests (what the value of X is). If X is less than 30 minutes it is faster. If X is longer than 30 minutes it is slower.

This means that the techniques, technologies & fluency of the programmer all affect the result of this equation. So it is not a clear cut answer & it will vary depending on the individual.


For me, it is often quicker to write the test. I have the advantage of years of fluency and tools like approval tests. However, the interesting point to me is while Test After means:  writing tests takes more time

Test  First means: writing tests may or may not save you time

I believe this possibility is worth exploring.

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