Abstract Test Cases (ATCs) have been widely used in practical scenarios such as combinatorial testing. When the set of ATCs is constructed, Test Case Prioritization (TCP) is applied to improve the testing quality. Among the many TCP approaches for ATCs, one intuitive and well-studied approach is Interaction Coverage Based Prioritization (ICBP), which greedily identifies one element as the next ATC such that it covers the largest number of uncovered $\tau$-wise parameter-value combinations. When a $\tau$-wise value combination, $\mathrm{v}\mathrm{c}$, has been covered by the already-selected ATCs, it is generally believed that it may have no further role to play in the ICBP process. However, each already-covered $\mathrm{v}\mathrm{c}$ may provide some potential contributions for the interaction coverage of the strength higher than $\tau$. Motivated by this, we propose a new TCP approach to prioritize ATCs, Weighted Interaction Coverage Based Prioritization (WICBP). WICBP attempts to assign a weight to each $\tau$-wise value combination that has already been covered. The experimental results show that when using the same prioritization strength, WICBP is more effective than ICBP but maintains comparable testing efficiency. In addition, WICBP with lower prioritization strengths achieves surprisingly competitive (even better) performance compared with ICBP with higher prioritization strengths.

String validation routines have been widely used in many real-world applications, such as email validation and postcode validation. String test cases are adopted to test these validation routines, to identify potential defects and security risks. Random Testing (RT) is a well-known testing approach to randomly generate string test cases from the input domain (i.e., the set of all possible test inputs), which is simple to implement at a low cost. However, its testing effectiveness may be unsatisfactory for string validation routines. The main reason for this is that RT may have a high probability to generate invalid rather than valid string test cases, due to its randomness property. This research proposes a new RT approach based on the output types (i.e., valid and invalid strings) for string validation routines, namely Output-type-guided Random Testing (RT-O), which attempts to randomly generate both valid and invalid string test cases with a certain probability. This research performed an empirical study involving several real-world string validation routines collected from ten Java open-source projects, to investigate and compare testing performances of RT-O against the previous two widely-used RT methods. The results show that the generated string test cases by RT-O outperform test cases generated by other RT methods.