This paper proposes a single fault model for the faults of the expressions, including operator faults (operator reference fault--an operator is replaced by another, extra or missing operator for single operand), incorrect variable or constant, incorrect parentheses. These types of faults often exist in the software, but some fault classes are hard to detect using traditional testing methods. A general testing method is proposed to detect these types of faults. Furthermore the fault simulation method of the faults is presented which can accelerate the generating test cases and minimize the testing cost greatly. Our empirical results indicate that our methods require a smaller number of test cases than random testing, while retaining fault-detection capabilities that are as good as, or better than the traditional testing methods.