Imagine I am a new QA in the team, never worked with transactions. What would you tell me about monetary entities?

Money entities are objects that represent monetary amounts in a system, such as account balances, payment amounts, or product prices. It is important to understand that they cannot be treated as regular numbers due to the specifics of precision and currency.

Key points:

• Precision and data type: Special data types with fixed precision (e.g., decimal or BigDecimal) are usually used to store money to avoid rounding errors that often occur with float or double.
• Currency: A monetary amount is always associated with a currency. Conversion should be considered, and the currency should be stored explicitly.
• Transactions: When working with monetary operations, atomicity is crucial — either the entire operation succeeds, or it does not happen at all. This prevents balance desynchronization.
• Validation: Ensure that amounts are non-negative and that operations do not lead to negative balances (if prohibited by business logic).

Example: If you are testing money transfer between accounts, you need to verify that the amount was deducted from one account and added to the other, and that in case of a failure, the money was neither lost nor created out of nowhere.