A common but faulty rule of thumb for estimating software testing effort goes something like this: estimate testing time at one half, one-third or even one fourth of development time in order to arrive at the time it will take to fully test software.
However, you greatly risk underestimating testing effort following this flawed approach. Estimating testing time based solely on the time it takes to develop the software may not provide an accurate reflection of the testing effort required. Testing is a complex process that depends on various factors beyond just development time.
Here are some reasons why estimating testing time based on development time can be problematic, and some concepts that you should consider in order to build more accurate testing estimate:
Scope and Complexity of Software Interactions: The complexity of the software, the number of features, and the intricacy of interactions can significantly impact testing time. A simple application might have a quick development timeframe, but extensive testing may be needed due to complex interactions. Testing various scenarios, edge cases, and user interactions may significantly extend testing time.
Testing Types:Â Different types of testing, such as unit testing, integration testing, functional testing, security testing, and performance testing, have their own time requirements. The mix of testing types needed depends on the nature of the software, so planning for all types of testing required by your software is important to scope out up front.
Developer Experience Level: Take developer experience level into consideration. The number and severity of bugs discovered during testing can vary widely. A software application might appear to be developed quickly, but if testing uncovers numerous critical issues, the testing phase could be prolonged.Â
Incorporate Time for Regression Testing: Â Changes made during development might introduce new issues or affect existing functionality. Regression testing, which ensures that new features don’t break existing ones, can require substantial time, even if development was rapid. Development and testing are often iterative processes. Feedback from testing might require developers to revisit certain parts of the code, which can extend both development and testing time, so plan for regression testing time.
Test Environment Set up: Setting up and maintaining the testing environment, including hardware, software, and data, can impact the overall testing duration. If multiple testing environments are needed for differing customer customization levels, be sure that the time to configure and maintain multiple testing environments is included in testing effort estimates.
Test Case Preparation and Coordination: Coordinating between development and testing teams, writing and managing test cases, and ensuring proper communication can also affect testing timelines. The number and complexity of use cases should drive your estimation of testing coordination effort as well.
Due to these complexities, it’s recommended to estimate testing time separately, considering the factors mentioned above. The rule of thumb in software testing should be that the time required for testing can often be similar to or even greater than the time spent on development. As a best practice, use historical data from similar projects to get a better sense of testing durations.
Ultimately, close collaboration between development and testing teams, along with regular monitoring of progress, is essential to ensure that testing is comprehensive, issues are addressed, and the software meets quality standards before release.