added test for negative coefficient

src/test/py/test_read_math_function.py

@@ -67,6 +67,9 @@ class ReadFunction(unittest.TestCase):
     def test_easy_function_linear_constant_gets_simplified(self):
         self.assertEqual(simplify_easy_math_function("v", "42x+42^(2)+1-3*4/3"), [1761, "42x"])
 
+    def test_easy_function_linear_constant_gets_simplified_negative_coefficient(self):
+        self.assertEqual(simplify_easy_math_function("v", "-42x+42^(2)+1-3*4/3"), [1761, "-42x"])
+
 
 if __name__ == '__main__':
     unittest.main()