I think that I’ve done a good job writing my unit tests, but how do I know for sure? The goal of unit tests is to make sure that code properly fulfills requirements. All of the code. So, basically I want to make sure that every line of code I have written is doing what it’s supposed to do. Enter the concept of code coverage.
…When we implemented the convert_isbn_10_to_13() method, we decided to use a custom exception (FormatException) to indicate that there was something wrong with the ISBN-10 string that is provided as input.
def convert_isbn_10_to_13(isbn10_code_string: str) -> str:
if not ISBNValidator.validate_isbn10(isbn10_code_string):
raise ISBNValidator.FormatException(f"{isbn10_code_string} is not a valid ISBN-10 code string.")
From a design standpoint, this is a good thing, but it presents a small challenge when we think about how we might test it within the confines of the Python unittest framework. Luckily the developers of the unittest module thought of this and we can assert whether or not a particular function raises a particular exception.
Well, there appears to be a lot more to ISBNs than I originally thought! This is a great example of how curiosity can be a good catalyst for practice at times. As I mentioned in the last post, I found out that there is a way to convert the “old” ISBN-10 codes to the newer ISBN-13 format. What would our ISBN exercise be like if we couldn’t upgrade an old code to a new one?
…Now that we’ve constructed this ISBN validator to understand both ISBN-10 and ISBN-13 numbers, I thought it might be a good idea to make a more generic validate_isbn method that attempts to detect which type of ISBN we are dealing with and then calls the correct method to validate it. That way, anybody using our validator can just pass in a string and we’ll do our best to figure it out. This might be useful in a library where there are books that feature each type of ISBN.
As I’ve been progressing through the exercise of parsing ISBN numbers, I discovered that the ISBN-10 numbers that I’ve been parsing were phased out in 2007! I guess that too many people were writing books around the world and they were running out of numbers. To deal with the problem, the ISBN people created something called a ISBN-13 code that is… (wait for it) … 13 digits long instead of the 10 digits in the previous standard.
After learning this shocking information, I decided that it wouldn’t be proper to have an ISBN validator that was almost 15 years out of date, so I added support for ISBN-13 validation to my practice example.
…In the previous versions of the ISBN Validation Exercise, I had the “test” code embedded with the actual validator itself. For simplicity, I think this is was the easiest way for the author to present the exercise on Codementor. As a reminder, this is what the “inline” test code looked like:
def test_isbns():
isbn = "123"
assert ISBNExercise.validate_isbn10(isbn) is False
isbn = "0136091814"
assert ISBNExercise.validate_isbn10(isbn) is True
isbn = "1616550416"
...
Generally, it isn’t considered good design practice to embed testing code inside of an application, and since I’m getting a bit carried away with this example, I figured that I’d do a bit of refactoring to add a more robust series of tests using the Python unittest framework. For those of you who aren’t familiar with the concept of unit tests, or why they are helpful, there is a great post at RealPython that explains the concept, as well as how to use the unittest framework in Python.
In my previous post Practicing Python, I started work on this exercise at Codementor. I got a decent solution working, but it still had a few deficiencies. Namely:
One of my resolutions this year is to try to increase the number of opportunities I have to practice programming — something I really enjoy doing. Fortuitously, this article appeared in my inbox today, so I figured that I’d give it a whirl. All in all, it took me about 10 minutes to complete and helped me to reinforce some basic Python skills. It also will give me a change to experiment with a new code formatting plugin in WordPress. In the future I think that I’m going to post my practice sessions here.
This particular solution is focused on validating ISBN-10 codes and explores basic string slicing as well as the use of the modulus operator in Python. It was a nice diversion!
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