diff --git a/src/lib.rs b/src/lib.rs
index 9c1df62..c665c6c 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -29,6 +29,10 @@
 pub use error::Error;
 pub use jpeg::get_exif_attr as get_exif_attr_from_jpeg;
 
+#[cfg(test)]
+#[macro_use]
+mod tmacro;
+
 mod error;
 mod jpeg;
 mod util;
diff --git a/src/tmacro.rs b/src/tmacro.rs
new file mode 100644
index 0000000..2c8474f
--- /dev/null
+++ b/src/tmacro.rs
@@ -0,0 +1,47 @@
+//
+// Copyright (c) 2016 KAMADA Ken'ichi.
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions
+// are met:
+// 1. Redistributions of source code must retain the above copyright
+//    notice, this list of conditions and the following disclaimer.
+// 2. Redistributions in binary form must reproduce the above copyright
+//    notice, this list of conditions and the following disclaimer in the
+//    documentation and/or other materials provided with the distribution.
+//
+// THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+// ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+// ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+// FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+// OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+// HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+// LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+// OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+// SUCH DAMAGE.
+//
+
+// Macros for testing.
+
+macro_rules! assert_ok {
+    ($expr:expr, $value:expr) => (
+        match $expr {
+            Ok(v) => assert_eq!(v, $value),
+            r => panic!("assertion failed: unexpected {:?}", r),
+        }
+    )
+}
+
+// This macro is intended to be used with std::io::Error, but other
+// types with kind() will also work.
+macro_rules! assert_err_kind {
+    ($expr:expr, $kind:expr) => (
+        match $expr {
+            Err(e) => assert_eq!(e.kind(), $kind),
+            r => panic!("assertion failed: unexpected {:?}", r),
+        }
+    )
+}
diff --git a/src/util.rs b/src/util.rs
index 7aa7772..a73b67e 100644
--- a/src/util.rs
+++ b/src/util.rs
@@ -36,3 +36,39 @@ pub fn read16<R>(reader: &mut R) -> Result<u16, io::Error> where R: io::Read {
     try!(reader.read_exact(&mut buf));
     Ok(((buf[0] as u16) << 8) + buf[1] as u16)
 }
+
+#[cfg(test)]
+mod tests {
+    use std::io::Cursor;
+    use std::io::ErrorKind;
+    use std::io::Read;
+    use super::*;
+
+    #[test]
+    fn read8_len() {
+        let mut reader = Cursor::new([]);
+        assert_err_kind!(read8(&mut reader), ErrorKind::UnexpectedEof);
+        let mut reader = Cursor::new([0x01]);
+        assert_ok!(read8(&mut reader), 0x01);
+        let mut reader = Cursor::new([0x01, 0x02]);
+        let mut buf = Vec::new();
+        assert_ok!(read8(&mut reader), 0x01);
+        assert_ok!(reader.read_to_end(&mut buf), 1);
+        assert_eq!(buf, [0x02]);
+    }
+
+    #[test]
+    fn read16_len() {
+        let mut reader = Cursor::new([]);
+        assert_err_kind!(read16(&mut reader), ErrorKind::UnexpectedEof);
+        let mut reader = Cursor::new([0x01]);
+        assert_err_kind!(read16(&mut reader), ErrorKind::UnexpectedEof);
+        let mut reader = Cursor::new([0x01, 0x02]);
+        assert_ok!(read16(&mut reader), 0x0102);
+        let mut reader = Cursor::new([0x01, 0x02, 0x03]);
+        let mut buf = Vec::new();
+        assert_ok!(read16(&mut reader), 0x0102);
+        assert_ok!(reader.read_to_end(&mut buf), 1);
+        assert_eq!(buf, [0x03]);
+    }
+}