The Four Levels of Software Testing: Unit Test, Integration Test, System Test, Acceptance Test

Four Levels of Testing that guarantee the quality of Software

Software testing is an important phase of the software development life cycle. This is the phase where you detect bugs in your application. However, software testing is not all about bug fixing but a complex process of determining the quality of a product. We can also say software testing compares a software application against the requirements for which it was built.  

In the past, testing of software was done after completely developing the application. However, this makes bug fixing costly and inefficient. This lead modern software development models like Agile to use continuous software testing, unlike traditional waterfall models.

As humans, we all make mistakes within the development of software. Some of them may be expensive and dangerous. Therefore, software testing should be necessary within software engineering. Internal testers or external testers carry out the software testing operations and tasks during different levels of testing.

The modern software testing process mainly has four testing levels. The test levels are:

  1. Unit testing, 
  2. Integration testing, 
  3. System testing, 
  4. Acceptance testing. 

The four levels of software testing review the system’s specifications, design, and code. In software engineering, the software testers perform test operations in these four test levels before launching the final product.

This article will give you a comprehensive introduction to each level of software testing and is a follow-on of the best practices of software testing.

Unit Testing

What is Unit Testing?

Unit-testing, sometimes called Component Testing, is the first level out of the four software testing levels. At this level, a unit is a line of code, function, or an individual procedure since units are nothing but the software’s components. An object-oriented programming unit is regarded as a single method. In software engineering, another term for Unit testing is micro-level testing.

Why should Unit Testing is important?

Unit testing is crucial since it examines every individual component at the beginning of the software testing phase. Hence, it will check whether every component meets its requirement or not.  This type of testing allows us to maintain and reuse code while speeding up the software development lifecycle, reducing costs, and simplifying debugging.

What are the steps of Unit Testing?

There are several steps that we need to follow to gain effective testing results. They are:

  1. Planning the Unit testing procedures.
  2. Defining Unit test cases and using the AAA approach.
  3. Writing Testable Code and performing the test.

1. Planning the Unit Testing procedures

We should define the Unit Test Cases while reviewing and reworking the baseline of each unit.  During the planning step, make sure that you map the components within your software program into units. This will assist you in deciding the type of testing (i.e., state-based or interaction-based) you will need. Afterward, you will be capable of planning simple and readable tests. It is essential to differentiate unit tests from integration tests as the final task of this step.

2. Defining test cases and using the AAA approach

At this step, you will have to define the data you require to execute the test. The AAA refers to Arrange, Act, and Assert. First, configure the unit you need to test and use the System Under Test (SUT). In conclusion, this will assist you in examining the performance of the program and investigate the results.

3. Writing Testable Code and Performing Unit testing

Once you have written the test cases, you are ready to write the test code.

What are the Component Testing tools that you can use?

Parasoft Jtest is an open-source framework that simplifies the maintenance of unit tests. It provides many tools like JUnit, NUnit, JMockit, Emma, and  PHPUnit. The Java programming language uses JUnit. As a result, it is popular compared to the other tools. EMMA is capable of analyzing and reporting the code. PHP language uses an open-source toolkit for testing called PHPUnit.  

What are the advantages of Unit Testing?

  1. Reduction of the total cost of testing by detecting bugs early. As a result, fixing these bugs are simple and easy.
  2. With the execution of unit testing after implementing an app, the development process becomes agile. Therefore it is easier to make changes to the existing design and code.
  3. Simplifies and improves the refactoring of code.
  4. Simplifies the debugging process. For example, if a certain test fails, you only have to check the last changes made to the code.
  5. In general, unit tests are documented as test modules. Therefore a new developer or a software tester can learn the software and test it quite easily by reading them.  

What are Unit Testing best practices?

  1. Have a proper and definite test plan.
  2. Prepare an automation test plan.
  3. Isolate the test environment during the execution of the tests.
  4. Use a version control system.
  5. Use recently used data for testing.
  6. Write independent test cases.
  7. Focus on looping the test cases.

Integration Testing

What is Integration Testing?

Integration testing is the second of the test levels. Since this level comes after the Unit Testing phase, it tests a combination of the units. Integration testing allows communication, security, and solutions for network breakdowns. Software testers or test engineers perform and carry out these tests.

Integration testing determines the defects of the interface. There are some manual and automated methods that are used to execute the tests. They are:

  1. Black-box testing
  2. White-box testing
  3. Gray box testing

There are two types of integration testing. They are:

  1. Unit integration testing 
  2. System integration testing

Why should you make Integration Testing a part of your software test life cycle?

It is difficult to detect some errors while testing a single unit and are only surfaced when multiple units are used together. Unit testing fails to uncover these kinds of issues making integration testing the solution to discovering them. Another reason for integration tests is due to user requirements changing during the testing phase. Therefore, those changes need to be identified at the level of integration testing.  Interfaces of the final product, hardware interfaces may cause errors and exceptions. Integration testing is essential to minimize errors and exceptions.

What are the steps of Integration Testing?

  1. Plan and prepare an Integration Test Plan.
  2. Define integration test scenarios and test cases.
  3. Define test automation scenarios.
  4. Perform test cases.
  5. Outline the defects.
  6. Track and test the defects again.
  7. Continue the testing operations until the completion of integration testing operations.

What are the different Integration Testing techniques?

Big bang approach

The big bang approach, which is a commonly used approach in integration testing, is performed on all modules as a whole. It makes it easy to check whether the performance of the system is working as expected or not. But it is time-consuming and costly as it detects the defects later within the software development life cycle. Therefore, the Big bang approach is the best method for small systems.

Top-down approach

The top-down approach starts the flow from the top-level module to the bottom-level module. In other words, the top module performs unit testing and progresses downward through integrations. All the modules are integrated in the same manner. This is the approach used by the top-down software development process. Stubs are used to test the top-level modules.

Bottom-up approach

The bottom-up approach starts the flow from the bottom-level module to the top-level module. This is the testingtechnique used when bottom-up software development process is followed. This integration testing approach executes tests for all integrated modules, and finally, the entire system is tested as a whole. Dummy programs known as Drivers are used to test top-level modules.   

Hybrid approach

A combination of the top-down approach and the bottom-up approach is called the hybrid approach. This approach is also known as the sandwich approach in integration testing. It utilizes both stubs and drivers.

What are advantages to Integration Testing?

  1. Guarantees the performance of modules that we integrate.
  2. Checks defects in the interface while testing.
  3. Gives access to the API and other third-party tools.
  4. Improves the reliability of testing.
  5. Improves the coverage of testing.
  6. Effective and efficient.
  7. Covers most of the components of the system.

What are Integration Testing best practices?

  1. Prepare data accurately for the test levels
  2. Define the architecture document of integration testing properly.
  3. Automate the testing procedures.
  4. Recognize the critical units to prioritize when testing begins.
  5. Wait until completion of the unit tests and before beginning integration tests.
  6. Test all the interfaces in depth.

System Testing

What is System testing?

The system testing is the 3rd phase of the software testing levels. System testing tests the entire system in more detail. At this level of software testing, we carry out functional and non-functional tests. As a result, this leads to an increase in testing complexity. The reason behind performing a system test is to assess the end-to-end system specifications. In general, the software is only a single component of a broader computer system. For that reason, the software is integrated with other features of the computer system.

Why should we do System Testing?

System testing ensures the performance of the required operations and compatibility with the operating system. Most importantly, error fixing and specification identification are performed at this level by the software quality assurance team of software testers. It verifies the system meets business requirements, techniques, and functions before deployment. System Testing is called end-to-end testing, as the environment of testing simulates the production environment. Also, System Testing verifies the input to check the desired output.

Steps of System Testing

  1. Prepare a suitable testing environment.
  2. Prepare the test cases for the testing processes:
  3. Produce the data that is needed for testing purposes.
  4. Execute test cases. After that, outline the defects.
  5. Perform Regression testing to detect the complications of the testing processes and define them.
  6. Continue the tests until they are successful.

What are the different testing types of System Testing?

 The following testing types fall into the System Testing stage of the four main software testing stages.

  1. Usability Testing
    Usability Testing principally concentrates on the user’s ease of utilizing the software application and flexibility in handling management. In addition it focuses on the capability of the system to achieve all its objectives.
  2. Load Testing
    We all need to know the software application will perform successfully or not under real-life loads. Meanwhile, load testing helps us to make us aware on that concept.
  3. Regression Testing
    Regression Testing ensures that none of the modifications made throughout the development process have created new bugs. In addition, it verifies bugs have not been introduced in old functionality.
  4. Recovery Testing
    Recovery Testing exhibits the reliability and trustworthiness of the software. Moreover, it defines the capability to recover from the possible crashes of a software solution.
  5. Migration Testing
    Migration Testing guarantees the transfer of software from older system bases to modern system bases without complications.
  6. Functional Testing
    Functional Testing identifies missing or misunderstood business requirements and bugs. In addition, testers can create a list of extra functionalities the software could have to enhance its functionalities and usability during functional testing.
  7. Hardware/Software Testing
    Hardware/Software Testing directs the attention on the cooperations between the hardware and software during system testing.

What are the advantages of System Testing?

  1. Verifies the performance of the techniques and user requirements of the system.
  2. Helps to identify defects before user acceptance testing.
  3. Increases the confidence of the testing team when the tests are successful.
  4. Since the testing environment is similar to the production environment, it is easy for new testers and software developers to configure required activities.

What are System Testing best practices?

  1. Depend only on controlled test environment. Therefore, the environment will be secure.
  2. Define tests that cover every part.
  3. Perform regression rests.
  4. Do not allow programmers to write tests. Hire skilled software testers to perform testing activities, especially functional testing.
  5. Outline and report all tests.
  6. Outline and report all detected bugs.

Acceptance  Testing

What is Acceptance Testing?

Acceptance testing, the last testing level in the software test life cycle, makes the final product stable, which leads to the best user experience. The execution of three testing levels happens before the execution of this level. Due to that reason, the occurrence of errors and bugs is extremely low when you reach this level of software testing.In software engineering, another term for Acceptance testing is user acceptance test (UAT).

Why Acceptance Tests are important?

Acceptance Testing evaluates the system’s compliance with user requirements, business requirements, and owner requirements. An external team performs UAT to minimize bias. On the other hand, the acceptance test examines the functionality and performance of the final product. The client performs acceptance testing using requirement gathering, testing planning, and the Pareto principle.

Different types of acceptance tests

Basically, there are two types of acceptance testing. They are,

  1. Alpha testing
  2. Beta testing

Alpha testing focuses on the users and the internal testing team, while beta testing focuses on user devices. Acceptance testing can be performed either by internal acceptance testing or external acceptance testing criteria.

Advantages of Acceptance Testing

  1. Automation of acceptance tests.
  2. Functions that we need to test are well known.
  3. It allows us to monitor and measure the progress of testing.
  4. The user acceptance testing has well known criteria.
  5. Acceptance testing allows the user to participate in testing. As a result, it increases customer satisfaction.

Best practices for Acceptance Testing

  1. Identify internal and external users of the organization.
  2. Create the test cases in detail and document the identified test cases.
  3. Prepare a suitable environment for the user acceptance test.
  4. Triage the issues and prioritize them.
  5. Include negative test cases.
  6. Do not allow developers to proceed with the testing.

Four Levels of Software Testing Conclusion

Each stage of the Four Levels of Software Testing increases in complexity and amount of time required to complete

The four levels of software testing play an important role throughout the software development life cycle. There are different testing methods and different types of testing for all levels of testing. By using different levels of software testing, it makes the final product defect-free. These four test levels make the testing process easy and efficient. The software tested by using these four levels of software testing ensures reliability and high performance, especially when coupled with AccelaTest’s revolutionary Test Case Management Tool.