Software testing is the most important phase in any software development project, so that we can know whether our project or product is going to be successful or it will fail before it goes live.

We can define software testing as process use to identify the quality of developed computer software, so that the developer of software can compare the results produced by the finished software and the expected one.

Through testing we cannot get totally bug free software we cannot achieve complete correctness through testing, but at least we can find some defects, which are there in the software.

There are many, many different ways and levels to test software; here I am mentioning very basic and common levels of testing, which are usually done for all software. If the software is very complex or real time oriented than more levels can be added to the testing to achieve a reliable software product.

Broadly software-testing levels are categorized into three levels.

• Unit Testing

• Integration Testing

• System Testing

Unit Testing

In this phase of testing, separate units of software system are tested. This is also known as component testing in which each module is tested alone to find any error in its source code. Programmer performs this testing as part of the development life cycle. The prerequisite for this phase is Unit Test Plan, which should be written from Low-level design document.

Integration Testing

This testing is done to test the communication between different components of the software; all the modules that a program comprises are being bring together to test whether they are functioning in correct order with their counter part. Modules are typically integrated in a top-down, incremental fashion.

For some projects integration testing can further be divided into two levels:

– Assembly Integration Testing.
– System Integration Testing.

During assembly testing, the integration of the software components is tested. During system integration testing, the communication with external systems is tested. Integration Test Plan should be written from High Level design document.

System Testing

This level of testing is done to test the functionality of software as a complete system. System testing is entirely different then integration testing. In integration testing interaction of component are tested while in system testing interaction of complete software with the system is tested.

Besides system functionality and behavior, system testing may include testing configuration, throughput, security, resource utilization, and performance.

After testing levels we will come to test designs. As we all know, before developing any component for the software first we have to design it, same is the case with software testing, before going for testing any software we have to design tests for the system.

Two most common methods for test design are Black box testing and White box testing.

Black-box test design treats the system as a "black-box", so it doesn't explicitly use knowledge of the internal structure. Black-box test design is usually described as focusing on testing functional requirements.

White-box test design allows one to peek inside the "box”, and it focuses specifically on using internal knowledge of the software to guide the selection of test data. Synonyms for white-box include: structural, glass-box and clear-box.

Now we will discuss about some testing techniques, there are many testing techniques for testing any software, here I have mentioned some like:

• Regression Testing Regression tests are tests that are run more than once. If the product or their environments have changed since the last time a test was run, it may find a new bug. Regression tests may be automated or manual.

• Stress Testing Tests are run to determine if the software can withstand an unreasonable load with insufficient resources or extreme usage.

• Performance Testing Tests are run to determine actual performance as compared to predicted performance.

In the software market you can get many tools for software testing, depending on your system and budget you have to choose among many tools. Some of the tools are:

WinRunner
TeamTest
Silk Test
JTest, C++ Test
Junit.

The testing phase, which is the most important phase in the software cycle gets secondary treatment from developers and IT managers, nobody wants to go to the testing team, people are forced to go for testing in any software development team.
Still testing is the only way to determine whether an application will function properly before it is deployed.