During deployment, tests run on the source org differ from those run on which type of org?

In the context of deployment processes, the tests that run on the source org are meant to validate the changes in the environment where the development occurred. When a deployment happens, typically the tests that are executed in the source org will vary compared to those in the destination org, particularly due to differences in the data, configurations, and possibly even the installed packages or features available in the destination environment.

The destination org is the environment where the changes are being deployed. This org can have different configurations, data states, and even additional packages installed that were not present in the source. Because of these variations, any tests that run during the deployment might behave differently, yielding different results for the same code being tested. The deployment process may trigger tests to ensure that any changes do not break existing functionality, which can lead to discrepancies in outcomes based on the state of the destination org.

Understanding this distinction is vital for ensuring that the deployment process is reliable and that any issues are addressed before changes go live in a production environment. In contrast, tests executed on development orgs, source orgs, and sandboxes are more controlled, closely aligned with the development process, and do not usually reflect the nuances that may exist in the destination org.