So far, we have covered a lot of information at a cursory level.
To make it more clear, let's have a look at what happens to a concrete change as it propagates through the systems, using an example:
The development team has been given the responsibility to develop a change to the organization's system. The change revolves around adding new roles to the authentication system. This seemingly simple task is hard in reality because many different systems will be affected by the change.
To make life easier, it is decided that the change will be broken down into several smaller changes, which will be tested independently and mostly automatically by automated regression tests.
The first change, the addition of a new role to the authentication system, is developed locally on developer machines and given best-effort local testing. To really know if it works, the developer needs access to systems not available in his or her local environment; in this case, an LDAP server...