Why is it ineffective to estimate testing effort solely based on a percentage of development effort?

Estimating testing effort based solely on a percentage of development effort is ineffective primarily because the quality of the development estimate may be poor. Development efforts can be challenging to predict accurately due to various unpredictable factors, such as changes in requirements, unforeseen technical challenges, or inaccurate initial estimations. Poorly estimated development efforts can lead to equally misleading testing estimates if the testing effort is directly tied to those development figures.

By relying on such a method, testing activities might be undervalued or overestimated, resulting in inadequate allocation of resources or time for the testing phase, which could compromise the quality of the final product. Effective testing estimation should take into account the specific requirements and complexities related to the testing process rather than be a mere percentage of potential development costs or efforts. This helps ensure a more meaningful assessment of the resources and time required for the testing activities, leading to better outcomes in software quality assurance.