import unittest
import psycopg2
import pandas as pd
import decimal

class TestPostgresQuery(unittest.TestCase):
    @classmethod
    def setUpClass(cls):
        cls.connection = psycopg2.connect(
            host="localhost",
            user="agent",
            password="qwerty",
            dbname="testdb",
            sslmode="disable"
        )
        cls.cursor = cls.connection.cursor()

    def test_query_returns_correct_average(self):
        """Check that the query returns the correct average surfacearea for countries with surfacearea > 1000000."""
        with open("query.sql", "r") as file:
            user_query = file.read()

        # Use the reference solution
        solution_query = """
        SELECT AVG(surfacearea) FROM country WHERE surfacearea > 1000000;
        """
        self.cursor.execute(solution_query)
        expected_result = self.cursor.fetchone()
        expected_avg = expected_result[0]

        self.cursor.execute(user_query)
        user_result = self.cursor.fetchone()
        user_avg = user_result[0] if user_result else None

        # Compare as floats for tolerance
        if isinstance(user_avg, decimal.Decimal):
            user_avg_value = float(user_avg)
        else:
            user_avg_value = user_avg
        if isinstance(expected_avg, decimal.Decimal):
            expected_avg_value = float(expected_avg)
        else:
            expected_avg_value = expected_avg

        condition = user_avg is not None and abs(user_avg_value - expected_avg_value) < 1e-6
        _dynamic_test(
            self,
            condition,
            f"Correct average ({expected_avg_value}) returned for countries with surfacearea > 1000000.",
            f"Incorrect average. Expected {expected_avg_value}, got {user_avg}."
        )

def _dynamic_test(test_case, condition, success_message, failure_message):
    if condition:
        test_case._testMethodName = success_message
        test_case.assertTrue(True, success_message)
    else:
        test_case._testMethodName = failure_message
        test_case.fail(failure_message)

def normalize_text(text):
    text = text.lower()
    text = re.sub(r"\\s{2,}", " ", text)
    text = re.sub(r"\\s*([,:?])\\s*", r"\\1 ", text)
    return text.strip()

if __name__ == "__main__":
    unittest.main()


test_solution.py

Focuses on practical SQL skills for filtering data with WHERE, sorting results with ORDER BY, and summarizing information using GROUP BY and aggregate functions. Hands-on challenges reinforce each concept, preparing learners to analyze and summarize real-world datasets effectively.

Challenge: Surface Area Selection

Solution