Game some more test coverage

src/num.rs

@@ -30,6 +30,7 @@ pub enum FracOp {
 }
 
 impl Default for Sign {
+    #[cfg_attr(tarpaulin, skip)]
     fn default() -> Self {
         Sign::Positive
     }
@@ -159,6 +160,7 @@ macro_rules! impl_int {
                     self == 0
                 }
 
+                #[cfg_attr(tarpaulin, skip)]
                 fn max_value() -> $type {
                     <$type>::max_value()
                 }
@@ -251,6 +253,7 @@ macro_rules! impl_unsigned {
                             let (x, y) = (min(x, y), max(x, y));
                             Self::stein_gcd((y - x) >> 1, x)
                         }
+                        #[cfg_attr(tarpaulin, skip)]
                         _ => unreachable!(),
                     }
                 }