In risk-driven testing, test cases are generated and/or prioritized based on different risk measures. For example, the most basic risk measure would analyze the history of the software and assigns higher risk to the test cases that used to detect bugs in the past. However, in practice, a test case may not be exactly the same as a previously failed test, but quite similar. In this study, we define a new risk measure that assigns a risk factor to a test case, if it is similar to a failing test case from history. The similarity is defined based on the execution traces of the test cases, where we define each test case as a sequence of method calls. We have evaluated our new risk measure by comparing it to a traditional risk measure (where the risk measure would be increased only if the very same test case, not a similar one, failed in the past). The results of our study, in the context of test case prioritization, on two open source projects show that our new risk measure is by far more effective in identifying failing test cases compared to the traditional risk measure.