A generic Java implementation of Andreas Zeller's delta debugging algorithm from Simplifying and Isolating Failure-Inducing Input and Why Programs Fail.
Given an input that causes a failing/error condition, this implementation of a divide and conquer algorithm splits the input data into smaller sets of chunks and checks if the smaller input reproduces the failing/error condition with a smaller input. This ddmin implementation is written generically leaving the choice of both how to "chunk" the input and how evaluate it to the end user.
The TestHarness interface contains a method run, which should be implemented to return true if the test passes and false if the test fails (such as an error). The SimpleExample class shows an example of a test harness that "fails" for any input that contains an Integer object 1 and 3.
public class SimpleExample {
private static TestHarness<Integer> harness = new TestHarness<Integer>(){
@Override
public int run(List<Integer> input) {
if (input.contains(1) && input.contains(3)){
return FAIL; // fail if the input contains 1 and 3
}
return PASS;
}
};
public static void main(String[] args){
LinkedList<Integer> input = new LinkedList<Integer>();
input.add(1);
input.add(2);
input.add(3);
input.add(4);
System.out.println(DeltaDebug.ddmin(input, harness));
}
}
The result is the minimized set [1,3].
Chunking is how we define each element in the input set we pass to the ddmin algorithm. For example if we had an input XML file that crashes an XML parser we could chunk the input into a set of elements by considering each character as an element, but we might be able to be a bit more efficient by considering some of the semantics of XML and chunking based on XML structure. This implementation of ddmin uses Java generics so you can define chunking however you want.
The included XMLParserExample class shows how this implementation could be adapted to exercise an XML parser that contains a bug when parsing a certain kind of URL. The Why Programs Fail book contains an exercise to reduce an XML file containing the error triggering input to a reduced input that still triggers the bug. The buggy parser and test input can be downloaded here.
The interactive demo can be launched by double clicking on the demo.jar file or running java -jar demo.jar from the command line.
