19. A computer program product embodied on a computer readable medium and comprising code that, when executed, causes a computer to perform the following: access at least a portion of a program to be debugged; access a behavioral model of the at least a portion of the program; receive a failing input sequence from the at least a portion of the program; execute the failing input sequence stepwise in parallel on both the behavioral model and the at least a portion of the program; validate, after each execution, an expected behavior of the at least a portion of the program by executing test sequences constructed from the behavioral model, wherein the test sequences comprise model states and transitions; perform model mutation using mutation operators, for creating a hypothesis of faulty program behaviors; verify each faulty program behavior in the hypothesis using the model mutators; and assign a score to each faulty behavior, wherein the score comprises a percentage of executions of confirming sequences that match the faulty program behavior; and rank the scores for producing a ranked list of diagnoses, wherein the diagnoses correspond to the mutation operators.
19. A computer program product embodied on a computer readable medium and comprising code that, when executed, causes a computer to perform the following: access at least a portion of a program to be debugged; access a behavioral model of the at least a portion of the program; receive a failing input sequence from the at least a portion of the program; execute the failing input sequence stepwise in parallel on both the behavioral model and the at least a portion of the program; validate, after each execution, an expected behavior of the at least a portion of the program by executing test sequences constructed from the behavioral model, wherein the test sequences comprise model states and transitions; perform model mutation using mutation operators, for creating a hypothesis of faulty program behaviors; verify each faulty program behavior in the hypothesis using the model mutators; and assign a score to each faulty behavior, wherein the score comprises a percentage of executions of confirming sequences that match the faulty program behavior; and rank the scores for producing a ranked list of diagnoses, wherein the diagnoses correspond to the mutation operators. 20. The computer program product of claim 19 further comprising code that, when executed, causes a computer to: present the ranked list of diagnoses to a user.