Add a currently wrong test for narrow.

tests/tensor_tests.rs

@@ -1,3 +1,4 @@
+// TODO: Also test the cuda backend.
 use candle::{DType, Device, Result, Tensor};
 
 #[test]
@@ -106,3 +107,15 @@ fn softmax() -> Result<()> {
     );
     Ok(())
 }
+
+#[test]
+fn narrow() -> Result<()> {
+    let data = &[[[3f32, 1., 4.], [1., 5., 9.]], [[2., 1., 7.], [8., 2., 8.]]];
+    let tensor = Tensor::new(data, &Device::Cpu)?;
+    assert_eq!(
+        tensor.narrow(2, 1, 2)?.to_vec3::<f32>()?,
+        // TODO: this is broken at the moment!
+        &[[[1., 4.], [1., 5.]], [[9., 2.], [1., 7.]]]
+    );
+    Ok(())
+}