If you plan to expose your SAP Data (Table or Query Data) to external environment like UI5/Fiori or HANA, then you need to push your data in a form of API. By API we mean, using OData. OData will generate a service link that can be accessed via internet and can be used to perform CRUD operations
REST, or REpresentational State Transfer, is an architectural style for providing standards between enterprise systems, making it easier for systems to communicate with each other. REST-compliant systems, often called RESTful systems, are characterized by how they are stateless and separate the concerns of client and server.
ABAP Unit does not replace good system or integration testing, but it can prepare your code so that these tests can be successfully completed in a shorter time period.
ABAP Unit Test class, a simpler way to verify the behavior of our code. The unit test class not only check the code coverage but helps a developer to cover all possible scenarios of a code leading to more reliable code with less chances of rework.