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 the query selects only the 'name' column."""
        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 but got: {columns}"
        )

    def test_correct_rows_returned(self):
        """Check if query returns only countries from 'Central America' or 'North America' regions."""
        with open("query.sql", "r") as file:
            query = file.read()
        self.cursor.execute(query)
        rows = self.cursor.fetchall()
        result_names = sorted([r[0].strip() for r in rows])
        expected_names = sorted([
            'Mexico',
            'Paraguay',
        ])
        _dynamic_test(
            self,
            result_names == expected_names,
            f"Query returns only countries from 'Central America' or 'North America'.",
            f"Expected names: {expected_names}, got: {result_names}"
        )

    def test_or_operator_used(self):
        """Check that both 'Central America' and 'North America' regions are included in results."""
        with open("query.sql", "r") as file:
            query = file.read().lower().replace("\\n", " ")
        condition = ("or" in query) and ("central america" in query) and ("north america" in query)
        _dynamic_test(
            self,
            condition,
            "Query uses OR operator and includes both regions.",
            "Query must use OR operator and include both 'Central America' and 'North America' in WHERE clause."
        )

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

Learn the core fundamentals of SQL and relational databases. Understand how databases store and organize data, write basic SQL queries, work with tables and perform essential operations. Build a strong foundation for working with databases in backend development.

Challenge: America Regions Filter

Solution