TDD: Tests are Client Number 1

Part of the TDD process consists of writing failing tests before the code that will eventually make them pass. Test-first alone is not TDD per se, but it is a part of it.

When tests are written before production code, this has several beneficial effects. This comes from the fact that these tests have the same orientation toward the code that client code will have in the future. Tests are, essentially, the first clients of any behaviors they drive into the system. Continue reading “TDD: Tests are Client Number 1”

TDD and Dynamically-Typed/Interpreted Languages

One controversy in software development is the relative value of strong, static typing (as in compiled languages like Java) vs. dynamic typing (as seen in interpreted languages like JavaScript). No attempt will be made here to engage in this debate, but it is interesting to note the role of TDD in languages that are not statically typed. Continue reading “TDD and Dynamically-Typed/Interpreted Languages”

TDD and Naming Part 3: Customized Assertions

Unit testing frameworks, which are the most common tools used by developers to conduct TDD, come with pre-made assertions that can be used to verify the behaviors being specified. Typically, these include assertions such as:

“areEqual()” (value comparison)
“areSame()” (entity comparison)
“isNotNull()”
“contains()”

Developers should not limit themselves to these pre-made assertions. Continue reading “TDD and Naming Part 3: Customized Assertions”

TDD and Naming: Part 2

Tests often establish example values used to compare the behavior of the system with the actual behavior indicated in the requirements. For example, if we had a system behavior that converted a temperature expressed in Fahrenheit to one expressed in Celsius, then the test that specified this might have an assertion along these lines:

assertEquals(100, converter.fahrenheitToCelsius(212));

However the use of these values directly in the assertion sidesteps an opportunity to express the meaning of those values in the specification. Continue reading “TDD and Naming: Part 2”

The Relationship Between Acceptance Test-Driven Development and Design Patterns

I’ve written a chapter in my book on The Relationship Between ATDD and Design Patterns. Essentially, ATDD provides us with quality acceptance criteria in the form of test specifications. We can use these to design our code from a behavior point of view instead of from an implementation point of view.

Doing this makes for more testable code, a quality highly correlated with other code qualities we want – strong cohesion, loose coupling and no redundancy. Design patters provide us with a method for combining these high quality objects together through the Gang of Four’s mantra’s of designing to behavior, using variation and encapsulating variation – in this case variation of type.

In the Agile world where requirements evolve, ATDD and Design Patterns Thinking work together to enable emerging designs from emerging requirements.