Test case generation is a painstaking task in software testing and has a strong influence on the efficiency and the effectiveness of software tests. It is an important subject in software testing research that has led to the development of several tools and approaches over the decades. This paper presented a systematic mapping study to get an overview about the current studies of distinct techniques for generation of test cases automatically. The techniques presented in this paper are random-based methods, search-based methods and data mining-based methods. Each technique is explored briefly to give the basic idea behind it. In general, the paper's objective is to give an up-to-date introduction and short review of the research in generation of test cases automatically. Systematic mapping study is the process of finding and collecting as much literature as possible, provides a structure of the type of research reports and the results that have been published by categorizing them depending on specific search questions to provide a background for further research. This study was based on a comprehensive set of 85 papers published in conference and journals between 2002 and 2013 obtained after using multistage selection criteria in the field of automatic test cases generation. The results from our systematic mapping study include information about the researches techniques used to generate test cases automatically and types of coverage within a specific period that can help researchers in this field through providing an overview of the current researches in this area. Furthermore, it may serve as a first step towards a great explanation of the topic with the help of systematic literature review.