Parser testing represents the basis of compiler testing because the accuracy of parsing execution directly affects the accuracy of semantic analysis, optimization and object code generation. It should include tests for correct and expected, but also for unexpected and invalid cases. In this paper, techniques for testing the parser, as well as algorithms and tools for test sentence generation are discussed. Generation of negative test sentences by modifying the original language grammar is described. Positive and negative test cases generated by Grow algorithm and Purdom algorithm are applied to the testing of L-IRL robot programming language and obtained results are described in this paper.