Few words for a background.

The Java ^TM Compatibility Kit (JCK) is a test suite, used to verify if the Java standard is correctly implemented. The first JCK came out together with the first JDK from SUN, now this effort evolved into the industry-wide Java Community Process.

The JavaTest ^TM harness is a test monitor, used in first versions of JCK, then across multiple Java Technology Compatibility Kits (TCK), now evolved into a general purpose open source test harness.

How it started

With permission of Jonathan Gibbons, who was around when Java was born, here is his story of the JavaTest childhood:

JavaTest started round about JDK 1.0.2, JCK 1.0.2a was applet-based and did not use JavaTest;  JavaTest was introduced in JCK 1.0.2b.

It definitely was not the first application written in Java, but it is true that testing was important to Java from the beginning. JavaTest is sufficiently old that we had to develop many GUI widgets ourselves, and one of the early JavaTest developers (Tim Prinzing) went on to become a significant member in the Swing team. It is probably reasonable to say that Tim pioneered light-weight components.

Curious how it looked like back then at early JDK times ? Check here.

You can see that testing is one of keys that brought Java platform to where it is now. Java's way of compatibility testing, that is having high quality TCK required to pass to get Java logo,  is how Write Once Run Anywhere is achieved,  it is the cost of application portability and platform standardization.

On the road

Inspired by the conversation at David Herron's Blog, I was looking for analogy to illustrate the value of compatibility testing in the Java ecosystem, here it is - Java is a road, compatibility testing is its pavement. Applications are vehicles and the hard cover on the road makes it possible to drive fast. 

For Java ME platform, its fragmentation is a freedom to choose number of wheels, engine, use a bicycle or a truck. Another part, the 'dark side', is where the road cover has holes, caused by bugs in specification and implementations, test coverage problems. Services are built around the road to take care of vehicles and holes, like JDTS and Java Verified, while the road has its pavement (TCKs), differentiating it from deserts, forests and swamps.