added test for splitting linear function without added constant as well as corresponding functionality

src/main/py/read_math_function.py

@@ -56,5 +56,7 @@ def simplify_easy_math_function(type, function):
 
 def extract_constant(function):
     coefficient, constant = function.split('x', 1) if 'x' in function else (function, '')
-    constant = constant.lstrip('+')
+    if constant == "":
+        constant = constant + "+0"
+    constant = constant.lstrip("+")
     return [constant, f"{coefficient}x"]

src/test/py/test_read_math_function.py

@@ -42,6 +42,8 @@ class read_function(unittest.TestCase):
         self.assertEqual(extract_constant("42x+5"), ["5", "42x"])
     def test_extraction_linear_function_constant_without_math_operators_subtraction(self):
         self.assertEqual(extract_constant("42x-5"), ["-5", "42x"])
+    def test_extraction_linear_function_no_constant(self):
+        self.assertEqual(extract_constant("42x"), ["0", "42x"])
 
 if __name__ == '__main__':
     unittest.main()