Fix a couple more bugs, add a bunch of unit tests

src/ngraph/pass/dyn_elimination.cpp

@@ -265,7 +265,8 @@ static SlicePlan make_plan(const Shape& input_shape,
             int64_t min_real_end = (is_reverse ? -1 : 0);
             real_end = std::max(min_real_end, std::min(int64_t(input_shape[i_in]), real_end));
 
-            // Adjust the stride for backwards slicing.
+            // Ensure stride is not zero, and adjust it for backwards slicing.
+            NGRAPH_CHECK(strides[i] != 0);
             int64_t real_stride = std::abs(strides[i]);
 
             // Adjust for reversal if needed. This isn't quite as simple as swapping begin and
@@ -281,6 +282,13 @@ static SlicePlan make_plan(const Shape& input_shape,
                 p.reverse_axes.insert(i_out);
             }
 
+            // nGraph's slice op does not like it when end < begin, so we truncate for that case
+            // here.
+            if (real_end < real_begin)
+            {
+                real_end = real_begin;
+            }
+
             // Compute output dimension.
             size_t dim = (real_end <= real_begin
                               ? 0