import unittest
import psycopg2
import pandas as pd

class TestTask(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_selects_correct_columns(self):
        """Check that only 'name', 'region', 'capital' columns are selected and in correct order."""
        with open("query.sql", "r") as file:
            query = file.read()
        self.cursor.execute(query)
        columns = [desc[0] for desc in self.cursor.description]
        expected_columns = ["name", "region", "capital"]
        _dynamic_test(
            self,
            columns == expected_columns,
            "Selected columns are correct and in the right order.",
            f"Selected columns are not correct or not in the right order. Got: {columns}, expected: {expected_columns}."
        )

    def test_result_sorted_by_region_and_capital_desc(self):
        """Check that results are sorted by region DESC, then capital DESC."""
        with open("query.sql", "r") as file:
            query = file.read()
        self.cursor.execute(query)
        rows = self.cursor.fetchall()
        if not rows:
            _dynamic_test(
                self,
                False,
                "Result is not empty.",
                "Query result is empty, cannot check sorting."
            )
            return
        df = pd.DataFrame(rows, columns=[desc[0] for desc in self.cursor.description])
        # For sorting, None values are considered less than any string in DESC order
        def safe_str(x):
            # Place None after all strings in DESC order
            return (x is None, x)
        sorted_df = df.sort_values(by=["region", "capital"], ascending=[False, False], key=lambda col: col.map(safe_str))
        # Reset index for comparison
        df = df.reset_index(drop=True)
        sorted_df = sorted_df.reset_index(drop=True)
        is_sorted = df.equals(sorted_df)
        _dynamic_test(
            self,
            is_sorted,
            "Results are sorted by region and capital in descending order.",
            "Rows are not sorted by region and capital in descending order."
        )

    def test_query_returns_all_rows(self):
        """Check that the query returns all rows from the country table."""
        with open("query.sql", "r") as file:
            query = file.read()
        self.cursor.execute("SELECT COUNT(*) FROM country")
        expected_count = self.cursor.fetchone()[0]
        self.cursor.execute(query)
        result_count = len(self.cursor.fetchall())
        _dynamic_test(
            self,
            result_count == expected_count,
            "Query returns all rows from the country table.",
            f"Query does not return all rows. Got {result_count}, expected {expected_count}."
        )

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: Sort the Countries by Region and Capital

Solution