Add failing test case for incorrect multiplication

Author: Xendergo

src/algebraic_numbers.rs

@@ -202,7 +202,7 @@ fn sign_changes_at(
                 let degree = polynomial.degree().unwrap_or(0);
                 let s = Sign::new(&polynomial.highest_power_coefficient());
                 if degree.is_odd() {
-                    s.map(|| -s)
+                    s.map(|s| -s)
                 } else {
                     s
                 }
@@ -1885,6 +1885,20 @@ mod tests {
             make_sqrt(3, DyadicFractionInterval::from_int_range(bi(1), bi(2), 0)),
             make_sqrt(6, DyadicFractionInterval::from_int_range(bi(1), bi(10), 0)),
         );
+        test_case(
+            RealAlgebraicNumber::new_unchecked(
+                p(&[-1, 2, 4]),
+                DyadicFractionInterval::from_int_range(bi(-1), bi(3), 1),
+            ),
+            RealAlgebraicNumber::new_unchecked(
+                p(&[-1, 2, 4]),
+                DyadicFractionInterval::from_int_range(bi(-1), bi(3), 1),
+            ),
+            RealAlgebraicNumber::new_unchecked(
+                p(&[-1, -12, 16]),
+                DyadicFractionInterval::from_int_range(bi(5), bi(6), 3),
+            ),
+        );
     }
 
     #[test]