input: Write a function to identify and correct the syntax error in the provided Python program. The program should return the result of adding two numbers using a function. Assert test cases to validate the corrected program.
  assert func(4, 5)==9
  assert func(10, 20)==30
  assert func(0, 0)==0
  assert func(-5, 5)==0
  assert func(7, -3)==4
output: def func(a, b):
      return a + b