Predicting software testability can reduce costs and efforts. Cohesion, as one of software quality metrics, found to be good indicator for software testability. Although there is a good interest in software testability on the class level in the literature, software testability on the package level has not received the same interest. The paper investigates the relationship between a newly proposed package cohesion metric and software testing effort. The empirical analysis used data collected from five Java open source software systems for which JUnit test classes are available. The results show that as good the package cohesion is, as the less testing effort is needed. The stability of the correlations allows us to draw optimistic conclusions about its use as an indicator.