In this case you automatically made the first function independent of the DB. if you work internally with a Pandas DataFrame, then write separate functions to processes the DataFrame and to read/write it from/to the DB. Do separate the database access code from the data manipulation code. Structure your codeįirst things first: Don’t forget the “Separation of Concerns”, my favorite coding principle. This article gives you a simple method to create one. And I didn’t even mention the availability of the database, which should not influence the test. Furthermore, if your test also includes writing to a database table you definitely don’t want to modify production data during your test. production database, as its content is out of the control of the unit test suite. It is not a good idea to work on the “real” ie. In this particular case we want to specify all the data we have in the table. You want to test how well it works, assuming you have a total control of the surroundings. You also know that these tests are called “unit” for a good reason: you only want to test a specific piece of code. But I simply can’t resist to tell you how much easier it makes your life, especially when it comes to refactoring, or any other code changes.) (This post is not about why and how you need to write unit tests. You are a seasoned programmer, so you know that you need unit tests. We can check that they all have the same type and get an error if they are not.Let’s assume you wrote some Python code to manipulate data which is stored in an SQL table. In python, not all the elements of a list have to be of the In the code below, lst is bound to a list object. We will just use simple assert statements for automated tests. Those provide some output summarizing tests that have passed as well as those that failed. In larger projects, other testing harnesses are used instead of assert, such as the python unittest You just want to know when one of your testsįails. Up your output window with the results of automated tests that pass. ![]() Why doesn’t assert print out something saying that the test passed? The reason is that you don’t want to clutter Trouble tracing to the place where you had an error in your code. That fact right away than to have some unexpected result much later in your program execution, which you will have Will alert that you that some condition you assumed was true is not in fact true. Why would you ever want to write a line of code that can never compute anything useful for you, but sometimes causesĪ runtime error? For all the reasons we described above about the value of automated tests.
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