Add some unit tests for split_init. (#1190)

Author: sunfishcode

src/buffer.rs

@@ -22,3 +22,52 @@ pub(super) unsafe fn split_init(
     let uninit = slice::from_raw_parts_mut(buf_ptr.add(init_len), uninit_len);
     (init, uninit)
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_split_init() {
+        let mut input_array = [
+            MaybeUninit::new(0_u8),
+            MaybeUninit::new(1_u8),
+            MaybeUninit::new(2_u8),
+            MaybeUninit::new(3_u8),
+        ];
+        let input_array_clone = input_array.clone();
+        let input_array_ptr = input_array.as_ptr();
+        let output_array = [0_u8, 1_u8, 2_u8, 3_u8];
+
+        unsafe {
+            let (init, uninit) = split_init(&mut input_array, 0);
+            assert_eq!(init, &[]);
+            assert_eq!(uninit.len(), input_array_clone.len());
+            assert_eq!(uninit.as_ptr(), input_array_ptr);
+
+            let (init, uninit) = split_init(&mut input_array, input_array_clone.len());
+            assert_eq!(init, &output_array[..]);
+            assert_eq!(init.as_ptr(), input_array_ptr.cast());
+            assert_eq!(uninit.len(), 0);
+            assert_eq!(
+                uninit.as_ptr(),
+                input_array_ptr.add(input_array_clone.len())
+            );
+
+            let (init, uninit) = split_init(&mut input_array, 2);
+            assert_eq!(init, &output_array[..2]);
+            assert_eq!(init.as_ptr(), input_array_ptr.cast());
+            assert_eq!(uninit.len(), 2);
+            assert_eq!(uninit.as_ptr(), input_array_ptr.add(2));
+        }
+    }
+
+    #[test]
+    fn test_split_init_empty() {
+        unsafe {
+            let (init, uninit) = split_init(&mut [], 0);
+            assert!(init.is_empty());
+            assert!(uninit.is_empty());
+        }
+    }
+}