+++
title = "Things I Learnt The Hard Way - Tests Make Better APIs"
date = 2019-06-19
[taxonomies]
tags = ["en-au", "book", "things i learnt", "unit tests", "layers", "apis"]
+++
Testing things in isolation may give a better view of your APIs.
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After reading the [integration tests ](/books/things-i-learnt/integration-tests )
chapter, you may end up with the impression that I don't like unit tests[^1].
Actually, I think they provide some good intrinsic values.
For example, as mentioned before, they can provide a better look at the
adherence to the design.
But, at the same time, they give a better view of your internal -- and even
external -- APIs.
For example, you're writing the tests for the view layer -- 'cause, you know,
we write everything in layers; layers on top of layers[^2] -- and you're noticing
that you have to keep a lot of data (state) around to be able to make the
calls to the controller. Or that you have similar calls, but the parameters
are sometimes switched (say, one function gets a token and a user ID, and
another function gets a user ID and a token -- why?) That's a sign that you
may have to take a better look at the controller API.
Not only that, but take, for example, the fact that you're working on a
library -- which will be called by someone else -- and you're writing tests
for the most external layer, the layer that will be exposed by that library.
And, again, you're noticing that you have to keep a lot of context around,
lots of variables, variables coming from different places and similar calls
using parameters in different ways. Your tests will look like a mess, don't
they? That's because the API _is_ a mess.
Unit testing your layers makes you the _user_ of that layer API, and then you
can see how much one would suffer -- or, hopefully, enjoy -- using that.
[^1]: Again, let's ignore for a second that there are no "unit" in "unit
tests"...
[^2]: And layers all the way down, [like
turtles](https://en.wikipedia.org/wiki/Turtles_all_the_way_down).
{{ chapters(prev_chapter_link="/books/things-i-learnt/integration-tests", prev_chapter_title="Unit Tests Are Good, Integration Tests Are Gooder", next_chapter_link="/books/things-i-learnt/tests-in-the-command-line", next_chapter_title="Make Tests That You Know How To Run on the Command line") }}
