Re: Automatic way to test performance optimizations
On Wed, 27 May 2009, Philipp wrote:
In my code, I must sometimes implement peformance optimizations. By
definition, the functional behavior does not change through this,
which can be tested through the public interface (regression tests).
But I would also like to test, that the optimization is used in the
correct places. Even using reflection to gain private access to
fields, I find this is difficult without introducing code (e.g. flags)
which only use is testing.
As an example consider the below code found in Arrays.mergeSort of the
Sun JDK. How would you go about testing, that the insertion sort is
used in the correct cases?
In this specific case, i'd write a class which implemented Comparable and
counted the number of times compareTo was called. Something like:
public class Counter {
private int count;
public void incrment() {
++count;
}
public int getCount() {
return count;
}
}
public class CountingInteger implemente Comparable<CountingInteger> {
private Integer i;
private Counter ctr;
public CountingInteger(int i, Counter ctr) {
this.i = i;
this.ctr = ctr;
}
public int compareTo(CountingInteger that) {
ctr.increment();
return this.i.compareTo(taht.i);
}
}
Then i'd make an array of CountingInteger objects sharing a common
Counter, do the sort, and assert that the count is what i expected. I'd
have to work out what that would be ahead of time somehow, but that's not
too hard.
If you were sorting ints, or Strings, rather than objects, thought, you'd
be stuffed. I imagine a lot of cases you have in real life will be ones
thta aren't amenable to the above mocking approach.
tom
--
Come with me, and we'll go dreaming.