ICU user guide page (http://icu-project.org/userguide/dateTimezone.html) describe how to test time zone data update.
7. Download testtz.zip file from ftp://ftp.software.ibm.com/software/globalization/icu/tzdata and unzip.
8. Compile and run the test program to verify that the data file works.
There will probably be failures of tests that are run against the updated dat file due to change in rules for Daylight Saving Time.
The description is pretty old and the test code is not currently maintained, so I'm going to remove the section for now. But, we should have a test case automatically generated based on the diff from the previous tzdata. Some of our clients asked us if there are any test programs to verify each update in the past.
