Introduction to System Integration Testing (SIT)
System Integration Testing is a type of testing that is done on the complete system after the hardware and software modules of that system have been integrated. It is done to validate the behavior of the system and to check whether all the modules in the system are functioning suitably with one another. It is also done to preserve the data integrity between the modules in the system.
System Integration Testing (SIT) is carried out after the sub-systems have individually undergone Unit Testing and that testing has been passed. SIT then tests the system as a whole, after it has been integrated. The result of SIT is then passed on to User acceptance testing (UAT).
Benefits of System Integration Test
- SIT helps in detecting defects at an early stage. The defects found during SIT are sent back to be fixed by the development team. This helps in saving time and the cost of getting it fixed at a later stage, which can be more expensive.
- SIT helps in getting an early opinion on the acceptability of a module in the system.
- SIT helps in exposing the faults that can take place when integrated components interact.
- There are several modules in a system and unit testing all the modules individually takes time. Even if each unit is tested individually, even then there is a possibility that it can fail when integrated as a whole as there are many problems that ascend when sub-systems interact with each other.
Thus, SIT is essentially required to uncover and fix the issues before sending the system to the user.
Approaches for Performing SIT
Let’s look at the different approaches for performing SIT, let’s understand this one by one.
1. Top-Down Approach
This is an incremental approach, where the testing begins at the topmost module of an application. The functionality of the modules at a lower level is simulated with the help of stubs. The top module is integrated with the stubs of the modules at the lower levels, one by one to test their functionalities. Once each test is completed, the respective stub is replaced by the real module. This way of testing continues until the whole system is tested.
Advantage
- No need for drivers and the functionality of the system is used to specify the test cases.
Disadvantage
- There is a dependency on the availability of the functionality of the lower level modules.
- There can be a delay in testing as the real modules are substituted with stubs.
- Writing stubs is difficult.
2. Bottom-up Approach
This is an incremental approach, where first, the lowest level modules are brought together to form clusters. Then a driver is made to get the input and output of the test case. Then the cluster is tested. After the cluster is tested, the driver is removed, so that the cluster can be combined with the upper level. This way of testing continues until the whole system is tested.
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Advantage
- Stubs are not needed in this approach.
- Testing becomes easier as the process ascends because the use of drivers is reduced.
Disadvantage
- The most important module i.e. the UI is tested at the end.
3. Big Bang Approach
In this approach, the modules of the system are integrated only after all the modules are complete. After integration, testing is carried out on the whole system to check for its working.
Advantage
- Only one round of SIT is required.
Disadvantage
- It is difficult to find the root cause of an error.
Process of System Integration Testing
The most common method of performing SIT is through the Data-driven method as it requires the least usage of software testing tools.
In this method, primarily, a data exchange i.e. data import and export take place between the system modules and then the performance of each data field within the individual layer is observed.
Once the software has been integrated, there can be three main states of data flow:
1. Data State when Flowing within the Integration Layer
The integration layer acts as an interface between the data import and export. Basic knowledge of certain schema technologies is required for performing SIT at this layer.
Steps to perform SIT to validate the data exchange:
- Authenticate the data properties within this layer against the requirements documents.
- Validate the web service request.
- Run some unit tests to verify the data mappings and requests.
- Review the logs.
2. Data state when flowing within the Database layer
Basic knowledge of SQL is required for performing SIT at this layer.
Steps to perform SIT to validate the data exchange:
- Verify whether all the data has reached and has been committed from the previous level.
- Authenticate the table and column properties against the requirements documents.
- Verify the data validation rules and the constraints applied to the database.
- Check stored procedures for any data to be processed.
- Review the logs.
3. Data state when flowing within the Application layer
Steps to perform SIT to validate the data exchange:
- Check for visibility of the fields in the UI.
- Execute test cases, both positive and negative to confirm the data.
Example of SIT
To make SIT a little clearer, let us take an example of a company that is using software to store the employee details.
This software comprises of two screens in the UI namely Name Screen and Employee ID Screen, and it has a database called Database A. The details entered in Name Screen and Employee ID Screen are entered in the Database A.
After a few years, the company requires additional data from the employees. Thus, an enhancement is required and they develop an Address Screen with another database, Database B. Now, this system having Address Screen and Database B has to be integrated with the existing system, and then this testing done on the whole system for proper functionality is called SIT.
To conclude, SIT is an important part of our testing as it gives us the first impression of how well our application is running. It can be done by the means of different approaches and processes, and we can use whichever is suitable for our application.
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