Added unit tests for instantiate_not_contains

Author: jasigal

unit/Makefile

@@ -24,6 +24,7 @@ SRC += unit_tests.cpp \
        solvers/refinement/string_constraint_generator_valueof/get_numeric_value_from_character.cpp \
        solvers/refinement/string_constraint_generator_valueof/is_digit_with_radix.cpp \
        solvers/refinement/string_constraint_generator_valueof/is_digit_with_radix_lower_case.cpp \
+       solvers/refinement/string_constraint_instantiation/instantiate_not_contains.cpp \
        catch_example.cpp \
        # Empty last line