Metamorphic Testing

2022-01-03

Metamorphic tests are a special case of property-based tests. They allow developers to describe richer properties, such as symmetry or idempotency. This article explains what metamorphic tests are and how they differ from other property-based tests. The post also shows how metamorphic tests are relevant for testing web APIs. The provided code examples use pytest, Hypothesis, and FastAPI.

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Packaging Python Applications in 2021

2021-07-28

Application packages have different requirements based on the intended user audience. When distributing a Python script targeted at Python developers it may be reasonable to ask users to pip install a requirements file. For users unfamiliar with Python or without programming experience this may be tedious or entirely impossible. This article presents different ways to package Python software from Wheels to fully self-contained bundles.

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Coverage-guided Test Data Selection

2021-05-08

Getting your hands on real-world data to test your software is the real deal. Nothing comes closer to reality than feeding an application with actual data from the wild. But what if the amount of data is more than you can handle? There are limitations on how much time you can spend on test runs. Whether you are running tests on a developer machine or as part of a Continuous Integration system, you probably won't be able to crunch large amounts of data each time you make a code change. Sooner or later, you will be forced to shrink your test corpus to a more manageable size. This article presents an approach that uses code coverage metrics to determine a representative test data subset.

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Enforcing coding conventions with libCST and Fixit

2020-09-18

The process of computer programming is a highly manual task and therefore error prone. Development teams often agree on good practices in an attempt to reduce the error rate—with varying success. This article presents two tools in the Python ecosystem that can be used to detect violations of coding conventions and correct them automatically. This specific example will show a way to enforce timeouts for HTTP requests.

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Optimizing a PostgreSQL query – A case study

2020-09-09

Some time ago, I performed a bunch of performance optimizations for a customer. The following article presents my journey through a complex issue caused by a relatively simple SQL query. In the process, I show tools that can be used to discover such performance issues and I explain a thing or two about indexes in PostgreSQL. Enjoy!

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Real-world application refactoring using Sidecars and Stranglers

2020-08-21

It's easy to break up a monolithic application on the whiteboard. That's until you realize that your monolith lives in a complex landscape that limits the decisions you can make. This article presents the modularization of a monolithic application that faced these problems. Specifically, it shows how the Sidecar (opens new window) and Strangler (opens new window) patterns can be leveraged to solve complex authentication problems.

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Simplicity is key to successful software

2020-05-11

Software projects often finish late or with poor quality. A common reason for this is failure to manage complexity. This article explains why simplicity is a key factor for successful software projects and gives pointers at what levels complexity can be reduced.

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On long-term software stabilization

2020-05-04

Stabilization of software releases is a common practice in large-scale software projects. The idea that stabilization is synonymous to leaving a component untouched is dangerous, though. This article argues that a “lockdown” of software components is counter-productive for stabilizing systems that support complex business processes.^[1]

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Neglecting Software Maintenance Kills Projects

2020-04-27

Meir M. Lehman analysed a variety of software systems and derived a set of scientifically backed statements that became known as Lehman's laws of software evolution. Many of the laws are immediately relevant to software maintenance. This article presents some of the key findings of Lehman's research from the 1970s – 1990s and explains why neglecting maintenance efforts is expensive. It also makes a point that people are bad at software.

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Every pattern has its cost - An approach to simple systems design

2020-04-20

Every architectural pattern has its individual set of benefits and drawbacks. This article presents a simple approach to prevent overengineering.

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