Functional testing is the most basic and key test type in software testing, and its main purpose is to verify whether each function of the software system runs normally according to the requirements of the requirements specification. It focuses on "whether the software does what it should do". Functional testing is usually carried out after development and system testing, which is an important link to ensure software quality.

First, the basic process of functional testing

1. Understand the requirements document
The first step of functional testing is to carefully read and analyze the requirements documents (such as requirements specifications) and make clear the expected behavior and input and output conditions of each functional module. Testers need to communicate with product managers and developers to ensure consistent understanding of requirements.

2. Write test cases
Test case is the basis of executing test, which usually includes test case number, test scenario, preconditions, operation steps, expected results and so on. When writing test cases, all function points should be covered, and boundary values and abnormal situations should be considered.

3. Prepare the test environment and data
The test environment should try to simulate the usage scenarios of real users, including hardware, operating system, database, network configuration, etc. At the same time, it is necessary to prepare enough test data to cover various usage situations.

4. Execute test cases
Testers perform operations step by step according to test cases, and observe whether the actual output is consistent with the expected results. If any inconsistency is found, it should be recorded as a Bug and submitted to the development team for repair.

5. Defect tracking and regression testing
After the defect is submitted, testers need to track its processing progress and conduct regression tests after the repair is completed to verify whether the problem is really solved and ensure that no new problems are introduced.

6. Generate a test report
After all the tests are completed, sort out the test execution, defect statistics, coverage analysis and other contents, and form a test report for the project team to evaluate the software quality and whether it has online conditions.

Second, the main methods of functional testing

-Black box test method: regardless of internal structure, only pay attention to the relationship between input and output. Common testing techniques include equivalence class division, boundary value analysis, causality diagram and so on.

-Manual testing: Testers manually execute test cases, which are suitable for functional modules with high complexity and frequent changes.

-Automated testing: use testing tools (such as Selenium, Postman, etc.) to automatically execute test scripts, which is suitable for regression testing and highly repetitive test tasks, and improves efficiency and coverage.

Third, matters needing attention

-Testing should be involved as early as possible, and participating in requirements review will help to find potential problems in advance.
-Test cases should be repeatable and complete to avoid missing critical paths.
-Pay attention to communication and cooperation with the development team to improve the efficiency of defect repair.
-Continuous regression testing to prevent new functions from affecting old ones.

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As an important part of software quality assurance, functional testing directly affects the stability and availability of the final delivered products. Only through systematic and comprehensive functional testing can we ensure that the software not only "runs" but also "runs correctly". Therefore, the testing team should constantly optimize the testing process, improve the testing ability, and escort the high-quality delivery of software products.