added test for no x in function for sum_of_simplified_exponential_functions

src/test/py/test_read_math_function.py

@@ -94,6 +94,9 @@ class ReadFunction(unittest.TestCase):
     def test_simplify_product_function_3_multiplicators(self):
         self.assertEqual(simplify_product_function("p", "x*x*x"), ["x^3"])
 
+    def test_sum_of_simplified_exponential_functions_no_x(self):
+        self.assertEqual(sum_of_simplified_exponential_functions("se", "2^1+2^1"), "Der Ausdruck muss die Variable 'x' enthalten.")
+
 
 if __name__ == '__main__':
     unittest.main()