Error using local modules in documentation tests

I'm playing around with a small crate for 2D noise generation. Here is a simplified snippet of my "lib.rs" file:

pub mod my_math {
    pub struct Vec2<T> {
        ...
    }
    ...
}
pub mod my_noise {
    use num::Float;
    use std::num::Wrapping;
    use my_math::*;

    /// Gets pseudo-random noise based on a seed vector.
    /// 
    /// # Examples
    /// 
    /// ```
    /// use my_math::Vec2;
    /// 
    /// let v_seed = Vec2::<f32>::new_values(4.134, -23.141);
    /// let noise_val = get_noise_white(&v_seed);
    /// 
    /// assert!(noise_val >= 0.0);
    /// assert!(noise_val <= 1.0);
    /// ```
    pub fn get_noise_white(seed: &Vec2<f32>) -> f32 {
        ...
    }
}

However, when I run cargo test, I get the following error:

---- my_noise::get_noise_white_0 stdout ----

<anon>:3:9: 3:16 error: unresolved import my_math::Vec2. Maybe a missing extern crate my_math?

<anon>:3 use my_math::Vec2;

I have also tried other forms of the use statement in the doc comment, including use my_math::*; and use self::my_math::*;. If I remove the line entirely, then I get an error that Vec2 is undefined.

What is the correct way to do this?