test.dir seems not so popular

[sekikn]

According to "Tests" section in styleguide:

Use directories under the property test.dir for temporary data.

But this directory seems not so popular and test.build.data seems most widely used.

[sekikn@mobile hadoop]$ find . -name '*.java' -exec grep 'test\.dir' {} \; | wc -l
       7
[sekikn@mobile hadoop]$ find . -name '*.java' -exec grep 'test\.build\.dir' {} \; | wc -l
      24
[sekikn@mobile hadoop]$ find . -name '*.java' -exec grep 'test\.build\.data' {} \; | wc -l
     316

Which one should developers use?