<s>[INST] import math
import sympy
import cmath
import time
from sympy import Rational
from decimal import Decimal
import random
import statistics
import numpy as np

def main():
    start_time = time.time()

    # ... (rest of your code remains the same)

    end_time = time.time()
    print("Program ended in ", end_time - start_time, " seconds.")

main()

This is the beginning of a program I am writing. I have a function `main` that performs some task in the program. I have a start_time and end_time variable that calculates the time taken by the program to run. How can I use Python's `unittest` module to measure the execution time of my program and check if it's within a certain time limit?[/INST]