An extension of symbolic execution for programs involving contracts with quantifiers over large and potentially unbounded domains is described. Symbolic execution is used to generate, from a program, concrete test cases that exhibit mismatches between the program code and its contracts with quantifiers. Quantifiers are instantiated using symbolic values encountered during a set of exhibited runs. In this setting, quantifier instantiation is limited to values supplied to or produced by a symbolic execution. Quantifier instantiation is controlled by performing a matching algorithm that uses run-time values of input and program variables in order to guide and limit the set of quantifier instantiations. With a sufficient set of instances, test cases are derived that directly witness limitations of the auxiliary assertions.