If you're struggling with test 11, the test is:

1 0 1000000 -2000 1
Exact (up to 1e-14) answer is 0.00628318530714

If your solution passes this, it will most likely pass all tests :)

Thank you! This test helped me a lot. And I've got AC. (I used 'decimal' with 100 digits in Python and Newton-Cotes method with n=8.)