add period to msg, fix test_function old exception check

Author: machow

pythonwhat/check_funcs.py

@@ -370,7 +370,7 @@ def call(args,
 from pythonwhat.tasks import ReprFail, UndefinedValue
 from pythonwhat import utils
 def has_expr(incorrect_msg="FMT:Unexpected expression {test}: expected `{sol_eval}`, got `{stu_eval}` with values{extra_env}.",
-             error_msg="Running an expression in the student process caused an issue",
+             error_msg="Running an expression in the student process caused an issue.",
              undefined_msg="FMT:Have you defined `{name}` without errors?",
              extra_env=None,
              context_vals=None,

pythonwhat/test_funcs/test_function.py

@@ -454,7 +454,7 @@ def build_test(stud, sol, state, do_eval, eq_fun, feedback_msg, add_more, highli
     if do_eval:
 
         eval_solution, str_solution = getResultInProcess(tree = sol, process = state.solution_process)
-        if str_solution is None:
+        if isinstance(str_solution, Exception):
             raise ValueError("Running an argument in the solution environment raised an error")
         if isinstance(eval_solution, ReprFail):
             raise ValueError("Couldn't figure out the argument: " + eval_solution.info)