Add more writeLength tests

contracts/utils/contracts/test/TestLibBytes.sol

@@ -325,4 +325,18 @@ contract TestLibBytes {
         b.writeLength(length);
         return b;
     }
+
+    function assertBytesUnchangedAfterLengthReset(
+        bytes memory b,
+        uint256 tempLength
+    )
+        public
+        pure
+    {
+        uint256 length = b.length;
+        bytes memory bCopy = b.slice(0, length);
+        b.writeLength(tempLength);
+        b.writeLength(length);
+        assert(b.equals(bCopy));
+    }
 }

contracts/utils/test/lib_bytes.ts

@@ -1131,6 +1131,20 @@ describe('LibBytes', () => {
             );
             expect(result).to.eq(`${byteArrayLongerThan32Bytes}${byteArrayLongerThan32Bytes.slice(2)}`);
         });
+        it('should result in the same byte array if length is reduced and reset', async () => {
+            const byteLen = (byteArrayLongerThan32Bytes.length - 2) / 2;
+            const tempByteLen = new BigNumber(byteLen).dividedToIntegerBy(2);
+            return expect(
+                libBytes.assertBytesUnchangedAfterLengthReset.callAsync(byteArrayLongerThan32Bytes, tempByteLen),
+            ).to.be.fulfilled('');
+        });
+        it('should result in the same byte array if length is increased and reset', async () => {
+            const byteLen = (byteArrayLongerThan32Bytes.length - 2) / 2;
+            const tempByteLen = new BigNumber(byteLen).multipliedBy(2);
+            return expect(
+                libBytes.assertBytesUnchangedAfterLengthReset.callAsync(byteArrayLongerThan32Bytes, tempByteLen),
+            ).to.be.fulfilled('');
+        });
     });
 });
 // tslint:disable:max-file-line-count