When you are responsible for the quality of a data platform , your system contains most likely not only of databases, but also a ETL, OLAP and reporting components. Data platform also implies that a change in source data can hugely influence the output.
I will take you through the step we took to gain and keep control and explain why you should do it and how, with which set of tools.

First of all, you need to know what software, are on your system and what will be changed during a release. There are a lot of paid tools on the market, but a lot can be done for free.

The Second step to gain control is to master your data. Codes which changes without notice can have big impact. To check on a daily basis if your assumptions on the source data are still valid tSQLt, a test framework for sqlserver is very handy.
Being able to perform a regression test, whenever that is in your release cycle or on a daily basis is the step to remain in control. Here can come SSAS cube or excel come to the rescue.
Finally don’t forget crosschecks to make sure that no data from your source system is lost in the processing.