Add some tests for Limit, BytesMut and Reader (#785)

tests/test_limit.rs

@@ -0,0 +1,86 @@
+#![warn(rust_2018_idioms)]
+
+use bytes::{buf::Limit, BufMut};
+
+#[test]
+fn long_limit() {
+    let buf = &mut [0u8; 10];
+    let limit = buf.limit(100);
+    assert_eq!(10, limit.remaining_mut());
+    assert_eq!(&[0u8; 10], &limit.get_ref()[..]);
+}
+
+#[test]
+fn limit_get_mut() {
+    let buf = &mut [0u8; 128];
+    let mut limit = buf.limit(10);
+    assert_eq!(10, limit.remaining_mut());
+    assert_eq!(&mut [0u8; 128], &limit.get_mut()[..]);
+}
+
+#[test]
+fn limit_set_limit() {
+    let buf = &mut [0u8; 128];
+    let mut limit = buf.limit(10);
+    assert_eq!(10, Limit::limit(&limit));
+    limit.set_limit(5);
+    assert_eq!(5, Limit::limit(&limit));
+}
+
+#[test]
+fn limit_chunk_mut() {
+    let buf = &mut [0u8; 20];
+    let mut limit = buf.limit(10);
+    assert_eq!(10, limit.chunk_mut().len());
+
+    let buf = &mut [0u8; 10];
+    let mut limit = buf.limit(20);
+    assert_eq!(10, limit.chunk_mut().len());
+}
+
+#[test]
+#[should_panic = "advance out of bounds"]
+fn limit_advance_mut_panic_1() {
+    let buf = &mut [0u8; 10];
+    let mut limit = buf.limit(100);
+    unsafe {
+        limit.advance_mut(50);
+    }
+}
+
+#[test]
+#[should_panic = "cnt <= self.limit"]
+fn limit_advance_mut_panic_2() {
+    let buf = &mut [0u8; 100];
+    let mut limit = buf.limit(10);
+    unsafe {
+        limit.advance_mut(50);
+    }
+}
+
+#[test]
+fn limit_advance_mut() {
+    let buf = &mut [0u8; 100];
+    let mut limit = buf.limit(10);
+    unsafe {
+        limit.advance_mut(5);
+    }
+    assert_eq!(5, limit.remaining_mut());
+    assert_eq!(5, limit.chunk_mut().len());
+}
+
+#[test]
+fn limit_into_inner() {
+    let buf_arr = *b"hello world";
+    let buf: &mut [u8] = &mut buf_arr.clone();
+    let mut limit = buf.limit(4);
+    let mut dst = vec![];
+
+    unsafe {
+        limit.advance_mut(2);
+    }
+
+    let buf = limit.into_inner();
+    dst.put(&buf[..]);
+    assert_eq!(*dst, b"llo world"[..]);
+}