input: Write a python function to measure the execution time of a given function and print it.
  assert measure_execution_time(slow_function) == "Function took 5.0 seconds."
  assert measure_execution_time(fast_function) == "Function took 0.0 seconds."
output: import time
  
  def measure_execution_time(func):
      start_time = time.time()
      func()
      end_time = time.time()
      execution_time = end_time - start_time
      return f"Function took {execution_time:.1f} seconds."