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# Testing
===
<!-- .slide: data-state="standard" -->
## Basics of testing
### Mistakes *will* happen!
<div style="display: flex; justify-content: center; align-items: center">
<div>
<ul>
<li class="fragment">The more complex the code, the harder to keep an eye on everything.</li>
<li class="fragment">However, we can build safeguards against problems:
<ul>
<li class="fragment">Throwing exceptions</li>
<li class="fragment">Logging (intermediate) results</li>
<li class="fragment"><b>Writing tests</b></li>
</ul></li>
</ul>
</div>
<img src="./media/testing/Doh.png" width="250">
</div>
===
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## Why Test?
<div style="display: flex; justify-content: center; align-items: center">
<div>
<ul>
<li class="fragment">Preserve functionality
<ul>
<li>Detect (new) errors early</li>
<li>Avoid unexpected outputs</li>
</ul></li>
<li class="fragment">Help users
<ul>
<li>Verify correct installation</li>
<li>Ensure reproducibility</li>
</ul></li>
<li class="fragment">Enable developers
<ul>
<li>Manage complexity</li>
<li>Simplify refactoring</li>
<li>Facilitate collaboration</li>
</ul></li>
</ul>
</div>
<img src="./media/testing/experiment.webp" width="400" style="margin-left: 60px">
</div>
===
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## Test Types
<ul>
<span class="fragment fade-out" data-fragment-index="4">
<li class="fragment fade-up" data-fragment-index="1">Exceptions in the code base
<ul>
<li>Intended to handle "expected" problems</li>
<li>Sound an alarm as soon as the problem arises</li>
<li>Provide clear feedback to the user</li>
</ul></li></span>
<li class="fragment fade-up" data-fragment-index="2">Unit testing
<ul>
<li>Smallest possible unit (module)</li>
<li>No dependency on outside code...</li>
<li>(... replace them with mocks, stubs, etc.)</li>
</ul></li>
<span class="fragment fade-out" data-fragment-index="4">
<li class="fragment fade-up" data-fragment-index="3">Integration testing
<ul>
<li>Test interactions between units</li>
<li>Can be on small scales, system wide, ...</li>
</ul></li></span>
</ul>
===
<!-- .slide: data-state="standard" -->
## Testing frameworks
Most modern programming languages have good options to streamline testing
- Python: [Pytest](https://docs.pytest.org/en/7.3.x/)
- Java: [Junit](https://junit.org/junit5/)
- R: [testthat](https://testthat.r-lib.org/)
- Matlab: [Testing Frameworks](https://nl.mathworks.com/help/matlab/matlab-unit-test-framework.html?s_tid=CRUX_lftnav)
- Julia: [Test](https://docs.julialang.org/en/v1/stdlib/Test/)
- C++: [GTest](https://google.github.io/googletest/) (developed by Google) or [Catch2](https://catch2-temp.readthedocs.io/en/latest/index.html)
- etc.
===
<!-- .slide: data-state="standard" -->
## Testing metrics
#### Targets are arbitrary and indicative
<div style="display: flex; justify-content: center; align-items: center">
<div>
<ul>
<li class="fragment fade-up">Coverage
<ul>
<li>Proportion of code that is executed</li>
<li>Target >= 80%</li>
</ul>
</li>
<li class="fragment fade-up">Ratio (lines of code:lines of test)
<ul>
<li>Target: (1:3)</li>
</ul>
</li>
<li class="fragment fade-up">Metrics can be misleading
<ul>
<li>They do not measure quality</li>
<li>Don't get blindsided by hitting targets over writing good tests</li>
</div>
<img src="./media/testing/metrics.jpg" width="300" style="margin-left: 60px">
</div>
===
<!-- .slide: data-state="standard" -->
## Write Code
<pre><code class="bash" style="overflow: hidden;" data-trim class="bash" data-line-numbers>
$ mkdir pytest-example
$ cd pytest-example
</code></pre>
<div class="fragment">
Creating a file <code>example.py</code> containing
<pre><code class="python" style="overflow: hidden;" data-trim class="bash" data-line-numbers>
def add(a, b):
return a + b
def test_add(): # Special name!
assert add(2, 3) == 5 # What's `assert`? š¤
assert add('space', 'ship') == 'spaceship'
</code></pre>
</div>
<div class="fragment">
Chat with the python shell about <code>assert</code> ...
</div>
<div class="fragment">
<pre><code class="python" style="overflow: hidden;" data-trim class="bash" data-line-numbers>
>>> assert 1==1 # passes
>>> assert 1==2 # throws error
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AssertionError
</code></pre>
</div>
===
<!-- .slide: data-state="standard" -->
## Test!
<pre><code style="overflow: hidden;" data-trim class="bash" data-line-numbers="1|1-9">
$ pytest example.py
======================== test session starts ========================
platform linux -- Python 3.6.9, pytest-7.0.1, pluggy-1.0.0
rootdir: /home/ole/Desktop/pytest-texample
collected 1 item
example.py . [100%]
========================= 1 passed in 0.00s =========================
</code></pre>
===
<!-- .slide: data-state="standard" -->
## Breaking Things
<pre><code class="python" style="overflow: hidden;" data-trim class="bash" data-line-numbers>
def add(a, b):
return a - b # Uh oh, mistake! š±
def test_add():
assert add(2, 3) == 5
assert add('space', 'ship') == 'spaceship'
</code></pre>
===
<!-- .slide: data-state="standard" -->
## Testing Again
<pre><code style="overflow: hidden;" data-trim class="bash" data-line-numbers="1|2-8|9-17|18-20">
$ pytest example.py
======================== test session starts =========================
platform linux -- Python 3.6.9, pytest-7.0.1, pluggy-1.0.0
rootdir: /home/ole/Desktop/pytest-texample
collected 1 item
example.py F [100%]
============================== FAILURES ==============================
______________________________ test_add ______________________________
def test_add():
> assert add(2, 3) == 5
E assert -1 == 5
E + where -1 = add(2, 3)
example.py:6: AssertionError
====================== short test summary info =======================
FAILED example.py::test_add - assert -1 == 5
========================= 1 failed in 0.05s ==========================
</code></pre>
<ul>
<li class="fragment">šā<span class="fragment">Functions fail on first error</span></li>
<li class="fragment">But all test functions are executed</li>
</ul>
===
<!-- .slide: data-state="standard" -->
## Pytest wrap up
- pytest collects all files starting <code>test_</code>...
- ... and runs all test functions starting with <code>test_</code>
- The tests pass when they do not throw (assertion) errors
<pre style="width: max-content;"><code style="overflow: hidden;" class="python" data-trim class="bash" data-line-numbers>
def steal_sheep():
...
def paint_cows():
...
# optionally in another file:
def test_steal_sheep():
...
def test_paint_cows():
...
</code></pre>
===
<!-- .slide: data-state="standard" -->
## Take-away
- Use pure functions when possible š
- Do you remember what these are? š
- Testing does not have to be hard š
- You often test anyway, but then throw the test away š§
- Use pytest if programming with Python š
- You don't have to strive for šÆ% test coverage
- But be smart about what you are testing š§
- Aim for a balance between unit- and integration tests āļø
- Testing removes the dread of refactoring š
- Your future you (and others!) will thank you š
===
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## Test-Driven Development: FizzBuzz
<div class="r-stack">
<img src="./media/testing/fizz_buzz_1.svg">
<img class="fragment" data-fragment-index="1" src="./media/testing/fizz_buzz_2.svg">
<img class="fragment" data-fragment-index="2" src="./media/testing/fizz_buzz_3.svg">
<img class="fragment" data-fragment-index="3" src="./media/testing/fizz_buzz_4.svg">
<img class="fragment" data-fragment-index="4" src="./media/testing/fizz_buzz_5.svg">
<img class="fragment" data-fragment-index="5" src="./media/testing/fizz_buzz_6.svg">
</div>
<ul class="fragment">
<li>fizz_buzz() takes an integer argument and returns it, BUT</li>
<ul>
<li class="fragment" data-fragment-index="1">fails on zero or negative numbers</li>
<li class="fragment" data-fragment-index="2">instead returns "Fizz" on multiples of 3</li>
<li class="fragment" data-fragment-index="3">instead returns "Buzz" on multiples of 5</li>
<li class="fragment" data-fragment-index="5">instead returns "FizzBuzz" on multiples of 3 and 5</li>
</ul>
</ul>
===
<!-- .slide: data-state="standard" -->
## Test driven development assignment:
<ul>
<li>Create a test function that checks the rules of FizzBuzz:</li>
<ul>
<li>fails on zero or negative numbers</li>
<li>return "Fizz" on multiples of 3</li>
<li>return "Buzz" on multiples of 5</li>
<li>return "FizzBuzz" on multiples of 3 and 5</li>
<li>otherwise return itself</li>
</ul>
<li class="fragment">Paste your tests in the collab document, and discuss</li>
<li class="fragment">Now write a function code to make your tests pass</li>
</ul>
===
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## Take-away
- What did you think of this style of development?
- Was it easier or harder than just writing code?
- Would your code look different without the tests? <!-- .element class="fragment" -->
- For what kind of projects would it be (not) useful? <!-- .element class="fragment" -->
**Test-Driven Development (TDD) is an optional tool in your toolbox** š ļø <!-- .element class="fragment" -->
