input: Write a function to create a Python script that contains a function with two parameters and returns the sum of the two parameters. The function should be named "add" and should have two parameters, "x" and "y". The function should return the sum of "x" and "y".
  assert add(3, 4)==7
  assert add(0, 0)==0
  assert add(-1, 1)==0
  assert add(-5, -3)==-8
  assert add(10, -2)==8
output: def add(x, y):
      return x + y