An Introduction to Levels of Software Testing & Implications

Software testing is a process that consists of different levels of software testing, each with its own specific goal and purpose. In this article, we will discuss these levels and what they mean for you as a developer or QA professional working in the industry.

What are the different levels of software testing

Software testing can be broadly divided into four categories:

  • Unit Testing
  • Integration Testing
  • Acceptance Testing
  • Regression Testing

There is no strict demarcation between these levels of software testing, and their boundaries may vary from one organization to another. However, it is generally accepted that unit testing precedes integration testing, which in turn precedes acceptance testing. Regression tests are performed after new features have been added or change made in an existing system. Let us go through them one by one:

Unit Testing:

Unit testing is done by software testers and is the process of testing individual units of source code to detect software bugs. Unit tests are created by developers as they write their applications and should be run automatically during or after completion. Unit testing is performed by developers and is used to confirm that each unit of source code works as intended. A unit test can be written for a method, function, class, or subroutine; it verifies that when the method/function is called with certain input parameters it does what was expected (e.g., passes valid data from one piece of functionality to another).

Integration Testing: 

The second level is called integration testing, and it tests the interconnections between different parts of the software. Handled by testers, the integration tests ensure that different parts of an application work together properly, while system tests look at how everything works together as a whole. Integration tests are generally performed after unit testing and before system testing. Integration tests should focus on how the different parts of your application interact with each other and not focus on individual operations or functions. There are further four classifications of integration testing:

Top-down integration: You test higher units before checking the lower level i.e. the tester has to test from top to bottom of the software codes.

Bottom-up integration: On the other hand, in bottom-up integration, the performer tests in the opposite direction ― from bottom to top. One has to try lower units and then climb up to the higher components.

Big-bang integration: Big-bang integration testing refers to when all elements are tested concurrently in a single phase. It is also applicable for validating small scaled applications while bypassing the top-down and bottom-up models. The modules are executed at once, i.e., programming, and combining, & are tested altogether.

Mixed (sandwiched) integration: Available modules are being tested whether they belong to high or low code lines, meaning that unbiased priority is given by the performer. Unresponsive modules are simulated to determine how well the available code will work when coding is completed and combined with others' contributions.

System testing

The third level is called system testing which is done by a QA team. It tests how well all of the parts work together when you use them in combination with each other. System testing is a part of quality assurance in software engineering. It is the final level of testing that ensures that an application or system meets its requirements and performs correctly under normal usage. It is usually done by the programmer who developed the application or system.

Acceptance testing

Acceptance testing is performed to ensure that the software meets the customer's needs. It is usually performed by the customer's team (or by someone who will be using the software). The focus of acceptance testing is to discover defects that may keep a project from being accepted. Acceptance testing is used in agile environments where the customer approves each release before it goes live; this type of test focuses on making sure everything looks good from their perspective. In addition to these general types of tests, there are also different levels of tests for each type. For example, unit testing can be done on a simple level or an intensive level.

Summing Up:

In conclusion, we hope that you have a better understanding of the levels of software testing. These core concepts carry immense significance when it comes to software development and budget allocation of different testing stages. 

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