Add some integration tests

The included images are taken from the libtiff test suite.

tests/decode_images.rs

@@ -0,0 +1,57 @@
+extern crate tiff;
+
+use tiff::ColorType;
+use tiff::decoder::{Decoder, DecodingResult};
+
+use std::fs::File;
+
+#[test]
+fn test_gray_u8()
+{
+    let img_file = File::open("./tests/images/minisblack-1c-8b.tiff").expect("Cannot find test image!");
+    let mut decoder = Decoder::new(img_file).expect("Cannot create decoder");
+    assert_eq!(decoder.colortype().unwrap(), ColorType::Gray(8));
+    let img_res = decoder.read_image();
+    assert!(img_res.is_ok());
+}
+
+#[test]
+fn test_rgb_u8()
+{
+    let img_file = File::open("./tests/images/rgb-3c-8b.tiff").expect("Cannot find test image!");
+    let mut decoder = Decoder::new(img_file).expect("Cannot create decoder");
+    assert_eq!(decoder.colortype().unwrap(), ColorType::RGB(8));
+    let img_res = decoder.read_image();
+    assert!(img_res.is_ok());
+}
+
+#[test]
+fn test_gray_u16()
+{
+    let img_file = File::open("./tests/images/minisblack-1c-16b.tiff").expect("Cannot find test image!");
+    let mut decoder = Decoder::new(img_file).expect("Cannot create decoder");
+    assert_eq!(decoder.colortype().unwrap(), ColorType::Gray(16));
+    let img_res = decoder.read_image();
+    assert!(img_res.is_ok());
+}
+
+#[test]
+fn test_rgb_u16()
+{
+    let img_file = File::open("./tests/images/rgb-3c-16b.tiff").expect("Cannot find test image!");
+    let mut decoder = Decoder::new(img_file).expect("Cannot create decoder");
+    assert_eq!(decoder.colortype().unwrap(), ColorType::RGB(16));
+    let img_res = decoder.read_image();
+    assert!(img_res.is_ok());
+}
+
+// TODO: GrayA support
+//#[test]
+//fn test_gray_alpha_u8()
+//{
+    //let img_file = File::open("./tests/images/minisblack-2c-8b-alpha.tiff").expect("Cannot find test image!");
+    //let mut decoder = Decoder::new(img_file).expect("Cannot create decoder");
+    //assert_eq!(decoder.colortype().unwrap(), ColorType::GrayA(8));
+    //let img_res = decoder.read_image();
+    //assert!(img_res.is_ok());
+}