input: Write a function to efficiently determine the commission rate based on the given gross sales. The function will directly return the commission rate upon the first condition being satisfied. The function should have one argument, gross_sales, and return one output, commission_rate. Include asserts to validate the function with various test cases.
  assert determine_commission_rate(12000)==0.1
  assert determine_commission_rate(7500)==0.07
  assert determine_commission_rate(4000)==0.05
  assert determine_commission_rate(10000)==0.1
  assert determine_commission_rate(4999)==0.05
output: def determine_commission_rate(gross_sales):
      if gross_sales >= 10000:
          return 0.1
      elif gross_sales >= 5000:
          return 0.07
      else:
          return 0.05