More tests on out-of-range accesses around unsafe code.

src/endian.rs

@@ -130,4 +130,13 @@ mod tests {
     fn out_of_range() {
         BigEndian::loadu16(&[0x01, 0x02], 1);
     }
+
+    // "attempt to add with overflow" with the arithmetic overflow
+    // check, and "slice index starts at 18446744073709551615 but ends
+    // at 1" without it.
+    #[test]
+    #[should_panic(expected = "at")]
+    fn wrap_around() {
+        BigEndian::loadu16(&[0x01, 0x02], (-1isize) as usize);
+    }
 }

src/value.rs

@@ -229,6 +229,7 @@ fn parse_unknown<'a>(data: &'a [u8], offset: usize, count: usize)
 mod tests {
     use endian::BigEndian;
     use super::*;
+    use super::parse_short;
 
     #[test]
     fn byte() {
@@ -448,4 +449,12 @@ mod tests {
             }
         }
     }
+
+    // These functions are never called in a way that an out-of-range access
+    // could happen, so this test is hypothetical but just for safety.
+    #[test]
+    #[should_panic(expected = "index 5 out of range for slice of length 4")]
+    fn short_oor() {
+        parse_short::<BigEndian>(b"\x01\x02\x03\x04", 1, 2);
+    }
 }