How to make sure that my tests are 'Behavioral' and 'Structure-insensitive'

Kent Beck pointed out at his desired test properties, that tests should be:

• Behavioral - tests should be sensitive to change in the behavior of the code under test. If the behavior changes, the test result should change.
• Structure-insensitive - tests should not change their result if the structure of the code changes.

Making sure, that these properties hold, is very easy. I check that:

• When I add/remove behavior I must perform changes in the test-files as well
• When I change the structure, I don't touch the test files

These are powerful heuristics.