input: Write a python function to generate the Fibonacci series up to N terms.
  assert fibonacci_series(5) == "Series up to 5 terms: 0 1 1 2 3"
  assert fibonacci_series(10) == "Series up to 10 terms: 0 1 1 2 3 5 8 13 21 34"
  assert fibonacci_series(0) == "Series up to 0 terms: "
output: def fibonacci_series(n):
      if n <= 0:
          return f"Series up to {n} terms: "
      fib_series = [0, 1]
      while len(fib_series) < n:
          fib_series.append(fib_series[-1] + fib_series[-2])
      return f"Series up to {n} terms: " + " ".join(map(str, fib_series[:n]))