Why this wierd error when I write test case in unit tests

require 'test_helper'

class StudentTest < ActiveSupport::TestCase
  fixtures :all
  # Replace this with your real tests.
  test "the truth" do
    assert true
  end

  def test_payment_for_invalid_student

    # Simulate a POST response with the given HTTP parameters.
    post_url = '/payments'
    #get :payments
    get('/students')
    #post(post_url, :payments => { :amount_paid => 200283, :create_on => Time.now, :student_id => 10000 })


    #assert_post_form form_url
    #assert_field form_url, :text, :model_object, :field_name
    #assert_field form_urm, :text, :model_object, :other_field
    #assert_submit form_url, 'Submit'


    # Assert that the controller tried to redirect us to
    # the created book's URI.
    #sassert_response :error

    # Assert that the controller really put the book in the database.
    #assert_not_nil Book.find_by_title("Love Hina")   

  end
end

  1) Error:
test_payment_for_invalid_student(StudentTest):
NoMethodError: undefined method `get' for #<StudentTest:0xb6e38404>
    /test/unit/student_test.rb:15:in `test_payment_for_invalid_student'

3 tests, 2 assertions, 0 failures, 1 errors
rake aborted!
Command failed with status (1): [/usr/bin/ruby1.8 -I"lib:test" "/usr/lib/ru...]