Programs for Programmable Logic Controller (PLC) are often written in graphical or textual languages. Control engineers design and use them in systems where safety is vital, such as avionics, nuclear power plants or transportation systems. Malfunction of such a computer could have severe consequences, therefore thorough testing of PLCs are important. The Base Choice (BC) combination strategy was proposed as a suitable technique for testing software. Test cases are created based on BC strategy by varying the values of one parameter at a time while keeping the values of the other parameters fixed on the values in the base choice. However, this strategy might not be as effective when used on embedded software where parameters need to be set for a certain amount of time in order to trigger a certain interesting behavior. By incorporating time as another parameter when generating the tests, the goal is to create a better strategy that will increase not only code coverage but also fault detection compared to base choice strategy. Timed Base Choice (TBC) coverage criteria is an improvement upon the regular Base Choice criteria with the inclusion of time. We define TBC as follows: The base test case in timed base choice criteria is determined by the tester of the program. A criterion suggested by Ammann and Offutt is the “most likely value” from the point of view of the user. In addition, a time choice T is determined by the tester as the most likely time for keeping the base test case to the same values. From the base test case, new test cases are created by varying the interesting values of one parameter at a time, keeping the values of the other parameters fixed on the base test case. Each new test case is executed with the input values set for a certain amount of time determined by the time choice T. The time choice is given in time units. The research questions stated in this thesis are as follows: Research Question 1 (RQ1) How does Timed Base Choice tests compare to Base Choice tests in terms of decision coverage? Research Question 2 (RQ2) How does Timed Base Choice tests compare to Base Choice tests in terms of fault detection? In order to answer these questions, an empirical study was made in which 11 programs was tested along with respective test cases generated by BC and TBC. Each program was executed on a PLC along with the belonging test cases and several faulty programs (mutants). From this testing we got the corresponding decision coverage for each program achieved by BC and TBC respectively as well as a mutation score measuring how many of the mutated programs was detected and killed. We found that TBC outperformed BC testing both in terms of decision coverage and fault detection. Using TBC testing we managed to achieve full decision coverage on several programs that we were unable to achieve using regular BC. This shows that TBC is an improvement upon the regular BC in both ways, thus answering our previously stated research questions.