input: Write a Python function to query customer details from a database where the country is 'Germany'.
  assert query_customers_from_germany() == [(1, 'John', 'Doe'), (2, 'Jane', 'Smith')]
  assert query_customers_from_germany() == [(3, 'Max', 'Mustermann'), (4, 'Erika', 'Mustermann')]
output: def query_customers_from_germany():
      import sqlite3
  
      # Establishing the connection to the database
      conn = sqlite3.connect('customer_database.db')
      cursor = conn.cursor()
      
      # Executing the query
      cursor.execute("SELECT * FROM customers WHERE country = 'Germany'")
      results = cursor.fetchall()
      
      # Closing the connection
      conn.close()
      
      return results