The main objective of the Testing Levels is to identify the missing areas in development and prevent the overlap or repetition between various phases of software development lifecycle, like requirement gathering and analysis, design, coding or implementation, testing and development. 

Each phase of the lifecycle goes through the testing process and so, to test all these phases in a justified manner, various testing levels are introduced. These testing levels are further explained in detail below.

Unit Testing 

Unit testing is basically done by the developers itself. They do this to make sure that the code they have written has no defects and meets the project requirements. In this level, developers test each piece of their code like classes, functions, interfaces and procedures. 

Component Testing 

This level is also known as Module Testing. Component testing is different from unit testing only because in unit testing the developers test their own piece of code while in component testing, the whole component is tested at once. This basically means that the software being developed is tested only after the whole component is built. 

For instance, if there is software which stores student record and has two main modules, where one saves their names and the other uploads their results, and then each module is tested separately. Hence, this method is known as component testing. 

Integration Testing 

While developing software application, if two modules of the software are integrated, Integration testing is done to test the behaviour and functionality of the integrated modules. There are many types of integration testing; some of the examples are given below 

  • Big Bang Integration Testing 
  • Top Down 
  • Bottom Up
  • Functional Incremental 

Sometimes, there can be several levels even within the integration testing. Most popular integration testing levels are 

  • Component Integration Testing: When two modules or components are integrated, then the type of testing done to test their behaviour and functionality is known as component integration testing. This testing is done to make sure the code does not have any side effects of integrating and performs as intended. 
  • System Integration Testing: Commonly referred to in its short form as SIT, this is an integration testing level where the testers test whether all the related systems maintain data integrity when put in a coordinated environment or not. 

System Testing 

In this level, testers basically test the compatibility of the software with its operating system. System Integration Testing or SIT is generally performed after the System Testing is done or parallel to it. 

Acceptance Testing 

The main objective of this level is to ensure that all the system and user requirements for developing the software are met. In this level, feedback and reviews are collected from the users and clients to check whether the software is performing among the live environment as intended. 

There are mainly two types of acceptance testing, which are 

  • Alpha Testing: This form of testing is done at the developer’s site. It usually takes place at the end of the development process to make sure the correct functionality of the software developed 
  • Beta Testing: This type of testing is done at the customer’s site. It is usually done before the product is finally launched