In order to help software managers and engineers allocate test resources in object-oriented software development, the Relative Test Complexity (RTC) metric was proposed and applied to an industrial system developed in C++. The initial validation by an engineering quality circle supported the validity of the RTC metric. In this paper, the RTC metric is further validated using actual fault data. It is shown that the RTC metric is a better surrogate of faults than Relative Complexity (RC), Harrison's Macro-Micro Complexity (MMC), McCabe's cyclomatic complexity (V(g)), Halstead's effort (E), and simple measures of size like LOC. Finally, the RTC and RC models are applied to change data with results that indicate that the RTC and RC metrics can be used to predict source code turmoil.