Merge rust-lang#122

122: Add sanity_check for atan2 r=japaric a=P1n3appl3

It's already been merged, but now I can say with certainty that this closes rust-lang#9 

Co-authored-by: Joseph Ryan <[email protected]>

Author: bors[bot]

src/math/atan2.rs

@@ -70,3 +70,13 @@ pub fn atan2(y: f64, x: f64) -> f64 {
         _ => (z - PI_LO) - PI, /* atan(-,-) */
     }
 }
+
+#[test]
+fn sanity_check() {
+    assert_eq!(atan2(0.0, 1.0), 0.0);
+    assert_eq!(atan2(0.0, -1.0), PI);
+    assert_eq!(atan2(-0.0, -1.0), -PI);
+    assert_eq!(atan2(3.0, 2.0), atan(3.0 / 2.0));
+    assert_eq!(atan2(2.0, -1.0), atan(2.0 / -1.0) + PI);
+    assert_eq!(atan2(-2.0, -1.0), atan(-2.0 / -1.0) - PI);
+}