Knowing the testing process and how it works is crucial for anyone looking to develop software. This paper highlights the four levels of testing in the software development lifecycle. It will also go into detail about the purpose for each level of testing, why testing on each level is important, and how the four testing levels relate to one another. Software testing is used to ensure that a piece of software functions exactly how it was designed to function and if there are any requirements or specifications set forth by a client, they are also functioning properly. The overall goal of software testing is not to discover every single bug that’s in a piece of software, but to reveal anything that will prevent the software from performing its desired function. Software can be tested by the developer but in some of the stages there are specialized test personnel whose sole job is to find problems with software before release to production. Below I will go into detail about the testing process:Unit TestingUnit testing only contains those attributes which are critical to the operation of a single unit. Unit testing allows the developer to alter the source code of a unit without concern for any other unit. Once many the units in a program are tested and are working as designed a larger segment of the program can be tested together with integration testing. Unit testing can become time-consuming and downright tedious at times especially on a large project. But, developers need to ensure they maintain all documentation of changes, and testing should be completed without the belief that software will be infallible. There is no way to test software for every possible real-world scenario. (Ritchie, S. 2013). On the website Excella Consulting Stephen Ritchie, states “If unit testing is written and performed properly and consistently, software projects are a lot more effective at delivering the correct solution in a predictable and managed way.” (Ritchie, S, 2013).Integration TestingIntegration testing is where programmers have the chance to combine all the units within a program and test them together. The main purpose of this test is to ensure when all the components are combined such as a software and hardware combination, they function correctly. It’s also beneficial since it reveals how efficiently each unit runs together, allowing for improvements to be made if it doesn’t meet the requirements. No matter how well one unit runs alone if it’s not incorporated correctly it may cause performance issues and errors. Integration testing is typically done in three ways. One way, “big bang” is where a programmer attempts to construct all the units at once, not testing any of them individually. This leads to an almost endless loop of errors as you will have a hard time isolating a problem, once you fix one issue you create another. A “top-down” approach has you integrate each unit moving downwards constructing the main command units and then subordinate units testing during each phase. “Bottom-up” integration has you testing units at the lowest level as each unit is integrated, the low-level units are combined to perform a sub function in the software. After the units are combined they are then tested before moving on. System TestingThis level is where the software is tested completely for the first time. The objective of this test is to assess whether the software aligns with what the client put down in their design request and to see if it meets the quality standards set forth before development began. System testing is typically performed by independent testers who had no role in the development process. System testing is one of the most important tests since is ensures the software meets the specifications, usage, and business needs that were requested by the client. The purpose of system testing according to the website inflectra.com which runs a test management software is “The system testing part of a testing methodology involves testing the entire system for errors and bugs. This test is carried out by interfacing the hardware and software components of the entire system” (Inflectra 2016). To summarize, system testing is the testing of the final product in an identical environment to production to ensure the software is ready for the client to test in acceptance testing.Acceptance TestingThe final testing phase is acceptance testing which is also referred to as user acceptance testing (UAT), this test is used to ensure that software is prepared for release into the production environment. Acceptance testing being the last step before the customer takes control of the software makes it the most important step in the process, the testing is typically performed by a quality assurance team. During the software development lifecycle, changes can be made to the software that do not align with what was expected by the client when they requested the software. With that in mind, during UAT the client tests the software to discern if the application meets the requirements they put forth before development began. After completing this step and if the software passed, the software will then be passed on to generation. The overall process of acceptance testing has a quality assurance team analyze the software’s performance during operation, and they discover and log bugs that cause the software to crash or generate errors.. In closingThese four tests were developed in this order to minimize the risk that software will have bugs when it launches into the production environment. Testing teams know how vital the testing phase is in the development lifecycle. Testing is done with progression of the software into production in mind starting with unit, integration, system, and finally acceptance testing. Each testing process is designed to efficiently examine the software and move it through the levels. There is no simple way to test a piece of software, this process was designed to make it easier on developers to fix software before it leaves their hands. After seeing the testing process, I see how important it is to detect problems before releasing software and to fix them on the spot during development. Overall, testing early and consistently on any project can help a developer discover problems in software before release to production and avoid money and time wasted later.