input: Write a function named generate_employee_table that takes a list of employee dictionaries as input and returns a string containing an HTML page with a table displaying the employee data. Each employee dictionary should have keys 'Name', 'Job Title', 'Department', and 'Salary'. Ensure the table is structured with headers for each column and that the salary is formatted as a string with a dollar sign and commas.
  
  assert generate_employee_table([
      {"Name": "John Doe", "Job Title": "Senior Developer", "Department": "IT", "Salary": 120000},
      {"Name": "Jane Doe", "Job Title": "Manager", "Department": "Finance", "Salary": 95000},
      {"Name": "Tim Smith", "Job Title": "Junior Developer", "Department": "IT", "Salary": 55000}
  ]) == '''<html>
    <head>
      <title>Employee Data</title>
    </head>
    <body>
      <table>
        <thead>
          <tr>
            <th>Name</th>
            <th>Job Title</th>
            <th>Department</th>
            <th>Salary</th>
          </tr>
        </thead>
        <tbody>
          <tr>
            <td>John Doe</td>
            <td>Senior Developer</td>
            <td>IT</td>
            <td>$120,000</td>
          </tr>
          <tr>
            <td>Jane Doe</td>
            <td>Manager</td>
            <td>Finance</td>
            <td>$95,000</td>
          </tr>
          <tr>
            <td>Tim Smith</td>
            <td>Junior Developer</td>
            <td>IT</td>
            <td>$55,000</td>
          </tr>
        </tbody>
      </table>
    </body>
  </html>'''
  
  assert generate_employee_table([]) == '''<html>
    <head>
      <title>Employee Data</title>
    </head>
    <body>
      <table>
        <thead>
          <tr>
            <th>Name</th>
            <th>Job Title</th>
            <th>Department</th>
            <th>Salary</th>
          </tr>
        </thead>
        <tbody>
        </tbody>
      </table>
    </body>
  </html>'''
output: 
  def generate_employee_table(employees):
      table_rows = []
      for employee in employees:
          table_rows.append(f"<tr><td>{employee['Name']}</td><td>{employee['Job Title']}</td><td>{employee['Department']}</td><td>${employee['Salary']:,.0f}</td></tr>")
      rows_html = "\n".join(table_rows)
      return f'''<html>
    <head>
      <title>Employee Data</title>
    </head>
    <body>
      <table>
        <thead>
          <tr>
            <th>Name</th>
            <th>Job Title</th>
            <th>Department</th>
            <th>Salary</th>
          </tr>
        </thead>
        <tbody>
  {rows_html}
        </tbody>
      </table>
    </body>
  </html>'''
  