A tester for testing a device under test is shown. The tester comprises a test unit configured for performing a test of the device under test using multiple test cases. Each test case may comprise variable values of a set of predetermined variables. The test units may be further configured to derive an output value for each test case indicating whether the device under test validly operates at a current test case or whether the device under test provides an error at the current test case. Furthermore, the tester comprises an evaluation unit configured for evaluating the multiple test cases based on a plurality of subsets of the predetermined input variables with respect to the output value. The subset of input variables may be smaller than the set of input variables. The evaluation unit may be further configured for providing a number of plots of the evaluation of the multiple test cases where each plot indicates the impact of one subset of the plurality of subsets of the predetermined input variables to the output value in dependence on respective relevance scores or associated with the respective relevance scores. The evaluation unit may be further configured to determine the relevance scores for the plurality of subsets of the predetermined input variables with respect to the output value, wherein the relevance scores indicate a respective relevance of each of the plurality of subsets for a determination of the impact of the subset of the input variables to errors of the device under test.