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_only_name_column(self):
        """Check that 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 does not select only the 'name' column. Columns selected: {columns}"
        )

    def test_returns_all_country_names(self):
        """Check that all country names are returned and match the initial data."""
        with open("query.sql", "r") as file:
            query = file.read()
        self.cursor.execute(query)
        result_rows = self.cursor.fetchall()
        result_names = sorted([row[0].strip() for row in result_rows])
        # Expected country names from init script
        expected_names = sorted([
            'Japan', 'Latvia', 'Mexico', 'Netherlands', 'Portugal', 'Sweden', 'Ukraine',
            'United States', 'Thailand', 'Paraguay', 'Philippines', 'New Zealand',
            'Norway', 'Monaco', 'Malta'
        ])
        # Remove trailing spaces from DB values, since 'name' is char(52)
        result_names_norm = [name.rstrip() for name in result_names]
        expected_names_norm = [name.rstrip() for name in expected_names]
        condition = result_names_norm == expected_names_norm
        _dynamic_test(
            self,
            condition,
            "Query returns all country names as expected.",
            f"Query did not return expected country names.\\nExpected: {expected_names_norm}\\nGot: {result_names_norm}"
        )

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: Find All Countries

Solution