A method of testing a target in a network by fault injection, includes: defining a transaction baseline; modifying at least one of an order and a structure of the transaction baseline to obtain a modified transaction with malformed grammar; and transmitting the modified transaction to a target. The method may further include, receiving a feedback from the target to determine fault occurrence. An apparatus for testing a target in a network by fault injection, includes: a driver configured to generate patterns, where a pattern can generate a plurality of packets for transmission to the target, the pattern being represented by an expression with a literal string and a wild character class; and a network interface coupled to the driver and configured to transmit and receive network traffic.