WebSphere Application Server V7.0: Concepts ... - IBM Redbooks

The system test environment can also be used by other teams. Perhaps the
system administrators need to test new patch levels for the operating system,
WebSphere Application Server, database, and so on before rolling them out in
production. The system test environment is a good place to do that. If a patch is
committed, it should also be applied to the other test environments to keep all
environments synchronized.
Acceptance test environment
The acceptance test environment is the last stage where testing takes place
before moving the application into production. The acceptance test environment
is the one that most closely resembles the actual production environment.
Hardware and software must be identical to the production environment.
Because of cost constraints, it is often not possible to have an acceptance test
environment with identical capacity as the production environment. The
acceptance test environment is, therefore, usually smaller than the production
environment, but needs to contain all the same components, same brands, same
software patch levels, and the same configuration settings as the production
environment.
The purpose of the acceptance test environment is to give the operations team a
chance to familiarize themselves with the application and its procedures (such as
installation, backup, failover, and so on). It also provides an opportunity to test
unrelated applications together, because previous environments focused on
testing the applications independently of each other.
Often the acceptance test environment is where performance tests are run,
because the acceptance test environment is the one most similar to the real
production environment.
When doing performance tests, it is extremely important to have a representative
configuration as well as representative test data. It is not unusual that projects
perform successful performance tests where the results meet the given
requirements, and then when the application is moved into production, the
performance is bad. This can be because the production database is much larger
than the databases used in the acceptance test environment. It is important that
the test databases be populated with representative data. Ultimately, a copy of
the production database should be used, but this may not be possible because
tests might involve placing orders or sending confirmation e-mails. Other causes
for differences in performance between the successful performance tests and the
production environment is, for example, that the performance tests ran without
HTTP session persistence, while the production environment uses session
persistence. To get realistic results, the performance test environment and setup
must be realistic, too.
300 WebSphere Application Server V7.0: Concepts, Planning, and Design