Add unit test for goto_trace_output in Makefile

Author: romainbrenguier

unit/Makefile

@@ -16,6 +16,7 @@ SRC += unit_tests.cpp \
        analyses/does_remove_const/does_expr_lose_const.cpp \
        analyses/does_remove_const/does_type_preserve_const_correctness.cpp \
        analyses/does_remove_const/is_type_at_least_as_const_as.cpp \
+       goto-programs/goto_trace_output.cpp \
        java_bytecode/java_bytecode_convert_class/convert_abstract_class.cpp \
        java_bytecode/java_bytecode_parse_generics/parse_generic_class.cpp \
        java_bytecode/java_object_factory/gen_nondet_string_init.cpp \