There are various reasons due to which Salesforce data can be lost, and they are as follows:
Altering the date and time
Converting parameters such as number and currency from other data types
Importing data that, at times, goes wrong
Moving the text, URL, or email from the text area
Altering the auto-number and the checkbox
Modifying the multi-select picklist to other types
Check out our blog to learn How to write test classes in Salesforce!