There are four different types of testing that can be performed on a software system. They are as follows.

1. Unit testing

2. Component testing

3. Integration testing

4. System testing.

1. Unit Testing:-  A unit is the smallest piece of source code that can be tested. It is also known as a module which consists of several lines of code that are processed by a single programmer. The main purpose of performing unit testing is to reveal that a particular unit doesn't fulfill the specified functional requirements and also to show that the structural implementation is not similar to the expected structure designed.

Unit tests can be both static tests and dynamic tests. At  first. static tests are performed followed by the dynamic tests to check the test paths, boundaries and branches. Most of the unit tests are dynamic white box structural tests. These tests require either the execution of the software as a whole or parts of software. If a bug is revealed while performing the unit test, it is referred to as a unit bug.

2. Component testing:-  Component testing is nothing but black box functional testing. This testing is used to test a single component or a group of components. A component is created by integrating one or more modules to form a single Target component. A module is a component and the function it calls is also a component. Thus, a component can either be an individual module or whole integrated system. Component testing is performed when a component doesn't match with its functional specification or its implementation structure, defined during preliminary test design. If such problems occur while performing the tests, they are referred to as component bugs. These bugs are eliminated by using necessary debugging tools.

3. Integration Testing:-  Integration is a process of combining smaller components to produce larger components. Integration testing is performed when the individual components undergo component testing successfully. But when components are integrated, component testing is either incorrect or  inconsistent. It also ensures that each individual component behave as per the specifications that are defined during test design. The main purpose of integration testing is to be detect the inconsistencies between these components. For example, A and B are components that have gone through component testing successfully, but failed when integrated.

Some of the situations where inconsistency arises are as follows,

(i) When there is an improper call or return statement.

(ii) When there is an inconsistent standard for data validation.

(iii) When an inconsistent method is used for handling the data objects.

Integrated objects testing is a higher level component testing compared to integration testing. The objective of integration testing is to wipe out the difficulties that occur while integrating individual components.

Following are the steps to perform integration testing,

(i) A and B components undergo component testing.

(ii) A and B are integrated to perform integration  testing.

(iii) The new integrated component [A, B] finally undergoes component testing.

4. System Testing:-  System testing exposes bugs that are not resulted from the components or from the inconsistencies between the components. System testing is a black box functional testing to test the entire software system. It is performed to show the behavior of the system. System testing is done either on the whole system that is integrated or only on the important parts of a system. During the test design, it ensures the systems's behavior as per the requirements specification. Testing is performed for the following applications like accountability, security, performance, sensitivity, configuration, start-up and recovery.