Stub and Driver are terms used in the context of integration testing, particularly in the incremental or top-down and bottom-up testing approaches. These terms represent components or modules that are used to facilitate testing when not all parts of the software are available or completed.
Stub:
A stub is a simplified or partial implementation of a software component or module that simulates the behavior of the missing or unfinished component. Stubs are used when the module being tested depends on another module that is not yet developed or available. The stub provides the necessary interface and returns predefined or dummy data to the calling module.
For example, in a banking software application, if the payment processing module is not yet implemented, a stub can be used to simulate payment processing and return a success message or a predefined result when called by other modules during testing.
Driver:
A driver is a program or module that is used to test a component that depends on another component that has not yet been implemented. Drivers provide the inputs and simulate the behavior of the missing component, allowing the component being tested to function as expected.
For example, if you are testing a user interface module that interacts with a database, but the database component is not ready, a driver can be used to provide the necessary data and simulate database interactions to test the user interface.
Top-Down Testing:
Top-down testing is an incremental approach to integration testing where testing begins with the highest-level modules or components in the software hierarchy and progressively integrates and tests lower-level modules. In this approach, stubs are used to simulate the behavior of lower-level modules that are not yet developed or integrated.
The goal of top-down testing is to verify the functionality of the top-level modules and their interactions before gradually incorporating lower-level modules until the entire system is tested.
Bottom-Up Testing:
Bottom-up testing is another incremental integration testing approach but starts from the lowest-level modules and gradually integrates and tests higher-level modules. In this approach, drivers are used to simulate the behavior of higher-level modules that are not yet developed or integrated.
The goal of bottom-up testing is to verify the functionality of the lower-level modules and their interactions before moving up to test the higher-level modules until the entire system is tested.
Both top-down and bottom-up testing approaches aim to identify integration issues and ensure that individual components work correctly when combined. The choice between these approaches depends on the software's architecture and the project's priorities. Some projects may even use a combination of both approaches, known as the sandwich approach, to achieve comprehensive integration testing.
