Unit testing and integration testing are the test methods used to verify the smooth functioning of the software. As the name suggests, unit testing verifies each software unit, component or module in isolation.
However, integration testing takes all the unit-tested components and integrates them to create a software architecture that dictates user-defined design. Let’s first begin with what software testing actually is.
What is Software Testing?
Software testing is an association of verification and validation. Verification refers to a set of tasks conducted to ensure that a specific function is correctly implemented in the software. On the other hand, validation includes a set of tasks conducted to ensure that the developed software meets the customers’ requirements.
- Verification – Are we developing the software right?
- Validation – Are we developing the right software?
Content: Unit Testing Vs Integration Testing
- Comparison Chart
- What is Unit Testing?
- What is Integration Testing?
- Key Differences
|Basis for Comparison
|It tests each module of the software in an isolation
|It tests the unit-tested components when they are brought together
|Unit testing is the first test conducted
|We conduct integration testing after unit testing but before system testing
|Performed by the software developers
|Performed by a separate team of testers
|Identifying errors is easy
|Identifying errors is comparatively difficult
|It focuses on testing the internal functionality of the module
|It focuses on testing the interfacing between the components
|Unit testing is an adjunct to the coding step. You can even parallelly test several components of the software
|We can perform integration testing only after all the components of the software are developed
What is Unit Testing?
Unit testing verifies the components or modules of the software in isolation. It tests the internal control paths of the module to detect errors within the boundary of that particular module. In unit testing, we can parallelly test multiple modules or components of the software.
The complexity of the unit testing and the errors it discovers is low. Because it only focuses on the module’s internal processing logic and data structure.
- We test the module’s interface to ensure that information smoothly flows in and out of the program unit. We have to exercise this test before we initiate any other testing. Because proper data flow across the module interface is necessary for all the data and other tests to be successful.
- Testing independent paths through the control structure ensures that all the instructions in the module have been executed. It uncovers errors that may occur due to erroneous computation, improper control flow, incorrect comparison, etc.
- We test logical data structure to ensure that the module maintains data integrity during all the steps of algorithm execution and that it does not impact the global data during the testing.
- Testing boundary conditions ensures that modules operate efficiently at their boundaries to limit or restrict their processing. Usually, software often fails at its boundaries.
Unit Testing Environment
Unit testing creates an environment to test each component or module of software in isolation. The software has several components, so we must develop a driver or stub software to test each. Each test case arrives with a set of expected results.
A driver is a program that accepts test case data and passes it to the component undergoing the test. Stubs are replacement for missing methods invoked by the components under test. They perform minimal data manipulation, prints verification of components execution, and return control back to component undergoing testing.
But if we observe carefully, these drivers and stubs are testing overheads. It takes effort and time to design/build them, but they are not delivered with the final software. Keeping the design of the driver and stub simple can reduce overhead, but it would not adequately unit test many of the software components.
So, sometimes unit testing is postponed until integration testing. Unit testing is preferable when developers design the component with high cohesion. It immensely reduces the number of test cases, and uncovers the errors easily.
Types of Unit Testing
There are two types of unit testing manual unit testing and automated unit testing.
- In manual unit testing, the test cases are run manually from the end users’ point of view.
- The test cases are run using specialized automated tools in automated unit testing. The quality of automated testing depends on how well the developers design test cases.
What is Integration Testing?
Sometimes, the unit-tested components that work well individually will also work when we put them together. It might happen that the data lost across the interface, a component puts an adverse effect on another, together they may not produce the desired result, etc.
Types of Integration Testing
We have three different types of integration testing
In the big bang, there is no prior testing. All the generated components incorporates to form a complete system and then tested to uncover the errors. Error correction is difficult as it becomes hard to identify the source of error in this method.
It starts with the main control module, and gradually incorporates rest of the modules by moving downwards through the control hierarchy. The modules subordinate to the main control module are incorporated in a depth-first or breath-first manner.
Bottom-up testing begins with integrating and testing the components at the lowest level of the program structure that performs a specific function. Thus, the test integrates the components, moving upwards in the program architecture.
Key Differences Between Unit Testing and Integration Testing
- Unit testing specifically tests each component of the software in isolation. However, integration testing tests the software components when they are brought together to build a program structure that dictates customer-defined design.
- Unit testing is the first test conducted that concentrates on verifying the software components or modules. On the other hand, integration testing is performed after unit testing, followed by system testing.
- Unit testing is performed by the software developers designing the components. On the contrary, there is a separate team of testers to perform integration testing.
- As unit testing focuses on the functionality of the components within its boundaries, identifying errors becomes easy. However, integrating the components can create chaos, such as data loss across the interface, adverse effects of one component on another, impact on global data structure, etc., making error detection difficult.
- Unit testing focuses on testing internal processing logic and data structure within the boundaries of the components. But, integration testing identifies the interfacing issues between the integrated components of the software.
- We can design unit testing alongside the coding steps, that is, before coding begins or after the source code generates. We can parallelly conduct unit tests on several components of the software. However, we perform integration testing only once all the components are ready.
- Cost to identify and fix the errors in unit testing is less than in integration testing because the object of unit testing (i.e. individual components) is comparatively smaller than integration testing (i.e. integrated components).
- Unit testing processes faster as compared to integration testing.
Unit testing and integration testing are the methods to verify and validate the software’s function and uncover its errors. Unit testing focuses on the functional verification of the components. However, Integration testing focuses on incorporating components into the software architecture.