import unittest
import psycopg2
import pandas as pd

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_selects_name_column(self):
        """Check if only the 'name' column is selected."""
        with open("query.sql", "r") as file:
            query = file.read()
        self.cursor.execute(query)
        columns = [desc[0] for desc in self.cursor.description]
        condition = columns == ["name"]
        _dynamic_test(
            self,
            condition,
            "Query selects only the 'name' column.",
            f"Query should select only the 'name' column. Columns found: {columns}"
        )

    def test_orders_by_name_ascending(self):
        """Check if results are ordered by name ascending."""
        with open("query.sql", "r") as file:
            query = file.read()
        self.cursor.execute(query)
        rows = self.cursor.fetchall()
        names = [row[0] for row in rows]
        sorted_names = sorted(names, key=lambda x: x.strip())
        condition = names == sorted_names
        _dynamic_test(
            self,
            condition,
            "Results are ordered by name ascending.",
            f"Results are not ordered by name ascending. Got: {names}"
        )

    def test_operates_on_country_table(self):
        """Check if query uses only rows from the country table by comparing count."""
        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())
        condition = result_count == expected_count
        _dynamic_test(
            self,
            condition,
            "Query returns the correct number of rows from country table.",
            f"Query should return {expected_count} rows, got {result_count}."
        )

    def test_no_syntax_error(self):
        """Check that the query executes without syntax errors."""
        with open("query.sql", "r") as file:
            query = file.read()
        try:
            self.cursor.execute(query)
            _dynamic_test(
                self,
                True,
                "Query runs without syntax errors.",
                "Query raised a syntax error."
            )
        except Exception as e:
            _dynamic_test(
                self,
                False,
                "",
                f"Query raised a syntax error: {e}"
            )

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 Countries in Ascending Order

Solution