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54 lines
3.8 KiB
Markdown
54 lines
3.8 KiB
Markdown
---
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title: When to use Unit-Tests?
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date: 2021-08-24
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tags: [programming]
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---
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We often talk about the importance of testing our programs, however many people don't mention at which point it is
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necessary to start and why sometimes it could just be a waste of time to implement unit-tests.
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## The purpose of unit tests
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The reason we use unit tests is simple, during our development, we're often actively changing things around and this
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has the potential to affect some unrelated functions in an unexpected way. This is by all means a human error, however
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it is very hard to prevent it and really most issues in development will be simple human errors. We simply won't expect
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that our changes could even remotely affect some other function and so we don't even think to check.
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This has lead to pushing broken code into production many times, and even for bigger companies, because however
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thorough the review process may be, it is possible that the reviewer will still simply miss something like this because
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it appears unrelated, the code is merged into a production branch and suddenly, your project breaks in production and
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you need to solve this issue very quickly, or roll back the changes.
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## When are they necessary?
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The goal behind unit tests is simply to run as much code as possible. In fact unit-tests are often combined with tools
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to tell you the code covered by them (one example of such tool is <https://coveralls.io>). We do this because this is
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precisely what the goal of unit-testing is, to run all of the code in a project.
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Unit-tests only become relevant when simply executing the project yourself doesn't automatically run every single line
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of code in your project. This is often the case when the program accept user input as a choice of some form, and so
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after a single run of the program, it would never get to the part behind the other choice. With a program as simple as
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this, with just 1 yes/no user choice, we still don't really need unit-tests though, because it's not a huge issue to
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simply run it twice and go through both of the options, but consider a program with 20 such choices, would you really
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be willing to go through all of this? Most people wouldn't and so the code remains not completely tested.
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The importance of running all of the code in a project is very high, especially for interpreted languages such as
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python or javascript. This is because the compiler won't warn you when it detects that something could be wrong with
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the code, with interpreted languages, that code isn't looked at until it's actually ran, so you might not notice it but
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you could simply have a typo in a variable name that would cause the whole thing to fail, but you won't find out by
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simply running it because you didn't go through the lines of code that had the actual issue in them.
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If you want to, in most modern languages, you can use a REPL (R: Read user input, E: Evaluate your code, P: Print out
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the result, L: Loop back to step 1) in which you can simply import your program and test individual functions yourself,
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this could be fine for some people and for smaller projects, but at this point you should already start asking yourself
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whether you want to be doing this for every submitted pull-request to ensure that it doesn't introduce any bugs, or
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whether you'd rather use an automated tool to do it for you.
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## Conclusion
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Unit-Tests are a neat tool and a great way to automate monotone testing of your application, but if your application
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runs every single line of code inside of it simply upon running it, there is usually no real reason to implement
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unit-tests and it would only clutter the project. However as your application starts to grow, and you start to have
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different branches your code can take, leading to some parts being left alone when ran in a certain way, that's the
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time to start thinking about whether you should implement unit-tests.
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