//! The mathematical constant tau.

extern crate core;

/// The mathematical constant [tau](http://tauday.com/),
/// where pi is defined as tau/2.
///
/// We provide it as `f64` for now.
///
/// ```rust{.example}
/// use std::num::FloatMath;
/// use tau::TAU;
/// assert_eq!(TAU.cos(), 1.0);
/// ```
#[unstable = "still waiting for associated constants"]
pub const TAU: f64 = core::f64::consts::PI_2;

#[cfg(test)]
mod test {
    extern crate core;
    use super::TAU;

    #[test]
    fn pi_is_a_derived_constant() {
        assert_eq!(core::f64::consts::PI, TAU / 2.0);
    }
}

//! The mathematical constant tau.

extern crate core;

/// The mathematical constant [tau](http://tauday.com/),
/// where pi is defined as tau/2.
///
/// We provide it as `f64` for now.
///
/// ```rust{.example}
/// assert!(tau::TAU / 2.0 == core::f64::consts::PI);
/// ```
#[unstable = "still waiting for associated constants"]
pub const TAU: f64 = core::f64::consts::PI_2;

--- 
+++ 
@@ -8,7 +8,20 @@
 /// We provide it as `f64` for now.
 ///
 /// ```rust{.example}
-/// assert!(tau::TAU / 2.0 == core::f64::consts::PI);
+/// use std::num::FloatMath;
+/// use tau::TAU;
+/// assert_eq!(TAU.cos(), 1.0);
 /// ```
 #[unstable = "still waiting for associated constants"]
 pub const TAU: f64 = core::f64::consts::PI_2;
+
+#[cfg(test)]
+mod test {
+    extern crate core;
+    use super::TAU;
+
+    #[test]
+    fn pi_is_a_derived_constant() {
+        assert_eq!(core::f64::consts::PI, TAU / 2.0);
+    }
+}
Change tests to work around rustdoc limitation on extern crate.
