Chapter 9: Levels of Testing

In Software development, both developers and testers work together to release a high-quality product. To release a high-quality product, every product goes through various testing processes. Coming to testing, testers use various levels of testing in the process of releasing a quality product. There are different levels of software testing. Each of these levels of software testing has a specific purpose. We will see each software testing level in detail.

Levels of Software Testing:

Let’s see what are the levels of software testing:

Different levels of software testing are as follows.

1. Unit Testing
2. Integration Testing
3. System Testing
4. Acceptance Testing

Let’s see the levels of testing in detail.


Unit Testing is done to check whether the individual modules of the source code are working properly. i.e. testing each and every unit of the application separately by the developer in the developer’s environment. It is AKA Module Testing or Component Testing


Integration Testing is the process of testing the connectivity or data transfer between a couple of unit tested modules. It is AKA I&T Testing or String Testing

It is subdivided into the Top-Down Approach, Bottom-Up Approach and Sandwich Approach (Combination of Top Down and Bottom Up). This process is carried out by using dummy programs called Stubs and Drivers. Stubs and Drivers do not implement the entire programming logic of the software module but just simulate data communication with the calling module.

Big Bang Integration Testing:

In Big Bang Integration Testing, the individual modules are not integrated until all the modules are ready. Then they will run to check whether it is performing well. In this type of testing, some disadvantages might occur like, defects can be found at the later stage. It would be difficult to find out whether the defect arouses in an interface or in a module.

Top-Down Integration Testing

In Top-Down Integration Testing, the high-level modules are integrated and tested first. i.e Testing from the main module to the submodule. In this type of testing, Stubs are used as a temporary module if a module is not ready for integration testing.

Bottom-Up Integration Testing

In Bottom Up Integration Testing, the low-level modules are integrated and tested first i.e Testing from sub-module to the main module. Same like Stubs, here drivers are used as a temporary module for integration testing.


It is called by the Module under Test.


It calls the Module to be tested.


It’s a black box testing. Testing the fully integrated application this is also called as an end to end scenario testing. To ensure that the software works in all intended target systems. Verify thorough testing of every input in the application to check for desired outputs. Testing of the users’ experiences with the application.


To obtain customer sign-off so that software can be delivered and payments received.

Types of Acceptance Testing are Alpha, Beta & Gamma Testing.

Alpha Testing:

Alpha testing is mostly like performing usability testing which is done by the in-house developers who developed the software. Sometimes this alpha testing is done by the client or outsiders with the presence of developers or testers.

 Beta Testing:

Beta testing is done by a limited number of end users before delivery, the change request would be fixed if the user gives feedback or reports defect.

Gamma Testing:

Gamma testing is done when the software is ready for release with specified requirements; this testing is done directly by skipping all the in-house testing activities.