Test Methodology

Articles about Test Methodology by Sebastian Bergmann

The image shows a close-up of printed financial data on paper, with multiple vertical columns of numbers in black, green, and red ink representing values such as prices or changes. A metallic pen lies diagonally across the sheet, suggesting analysis or review of the numerical information.

February 25, 2026

Replay Testing

Replay Testing leverages the memory of your event sourcing system to test new versions with real history and shows which oracles truly inspire confidence in your changes.

The image illustrates that valuable insights can be gained from recorded events through skilful processing and analysis, a metaphor for the value of event sourcing and automated testing in software development.

February 20, 2026

From Events to Insights

Event Storming, DDD, CQRS, and Event Sourcing are intertwined: the tests not only check the events, but also become living documentation and a bridge between technical expertise and code.

February 4, 2026

Data Provider or Properties?

One test, hundreds of inputs, and an automatic edge case search. But property-based testing has a hidden pitfall that many overlook.

The image shows a hand against a dark background, presenting a glowing light form that is drawn half like a brain, half like a light bulb. The scene conveys focused clarity and symbolises small inputs with great insight – fitting for shrinking in property-based testing.

January 28, 2026

Smaller input, greater insight

Shrinking is the unsung hero of property-based testing. I show you how it helps to make inevitable errors understandable.

January 21, 2026

Property-Based Testing

We only test what we think of. That is precisely what can become a problem.

The image shows an aircraft flight recorder, commonly known as a "black box", resting on the seabed under water. The cylindrical orange device is slightly rusted and mounted on a base plate, with a rectangular attached unit behind it. A large white label on the cylinder reads "FLIGHT RECORDER DO NOT OPEN".

December 17, 2025

A flight recorder for your code

Your PHP project has no tests and an upgrade is pending? The classic dilemma: to introduce tests, you have to change code – to change code, you need tests. How can you break this cycle? With characterisation tests.

The image shows two hands that seem to be forming a glowing light that appears magical. The person is wearing several rings and bracelets and has their arm tucked into a purple jumper. In the foreground is a table covered with a dark cloth, on which lie candles, coins, chains and a small bottle containing a blue-green liquid. The warmly lit scene evokes a spiritual or mystical atmosphere, reminiscent of a ritual or fortune telling.

December 10, 2025

Seeing the Truth: Test Oracles

Your tests are successful. But are they really? Without a suitable test oracle, you will never know.

This image illustrates the contrast between technical motivation, represented by flowing, dynamic data streams, and domain motivation, represented by solid, stable foundational concepts. This visual metaphor illustrates the main point that DTOs facilitate the movement of data between layers, while value objects represent unchangeable domain concepts that form the basis of business logic. The layered architecture also illustrates how these objects are used in different contexts: technical boundaries versus core business logic. It emphasises the stability and predictability that immutability brings to testing practices.

December 3, 2025

Testing with DTOs and Value Objects

Know the differences between data transfer objects and value objects and understand why immutability helps with testing.

This image shows a stylised representation of a DNA double helix, with a single section highlighted. The DNA strands are shown in blue, while a short section of the base pairs and the associated connections glow red. The imagery communicates a mutation or targeted change at the molecular level, as applied in genetic analysis, mutation testing or biotechnological processing. The focused area could symbolise a mutation, repair or targeted intervention, as used in genetic research.

November 19, 2025

Path Coverage or Mutation Testing?

How thoroughly do your tests cover the code, and how reliably do they detect real errors? I show you how to find out.

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