add basic test for stride constructor

Author: vbarrielle

src/dimension.rs

@@ -20,7 +20,10 @@ pub fn stride_is_positive(stride: Ix) -> bool
 /// Check whether the given dimension and strides are memory safe
 /// to index the provided slice.
 ///
-/// To be safe, no stride may be negative, and the 
+/// To be safe, no stride may be negative, and the offset corresponding
+/// to the last element of each dimension should be smaller than the length
+/// of the slice. Also, the strides should not allow a same element to be
+/// referenced by two different index.
 pub fn can_index_slice<A, D: Dimension>(data: &[A],
                                         dim: &D,
                                         strides: &D

tests/dimension.rs

@@ -4,6 +4,7 @@ use ndarray::{
     Array,
     RemoveAxis,
     arr2,
+    can_index_slice
 };
 
 #[test]
@@ -36,3 +37,14 @@ fn dyn_dimension()
     assert_eq!(z.shape(), &dim[..]);
 }
 
+#[test]
+fn slice_indexing_uncommon_strides()
+{
+    let v: Vec<_> = (0..12).collect();
+    let dim = (2, 3, 2);
+    let strides = (1, 2, 6);
+    assert!(can_index_slice(&v, &dim, &strides));
+
+    let strides = (2, 4, 12);
+    assert!(!can_index_slice(&v, &dim, &strides));
+}