Add test for unique_ptr.

tests/run/cpp_smart_ptr.pyx

+# mode: run
+# tag: cpp
+
+from libcpp.memory cimport unique_ptr, shared_ptr
+
+cdef extern from "cpp_smart_ptr_helper.h":
+    cdef cppclass CountAllocDealloc:
+        CountAllocDealloc(int*, int*)
+
+def test_unique_ptr():
+    """
+    >>> test_unique_ptr()
+    """
+    cdef int alloc_count = 0, dealloc_count = 0
+    cdef unique_ptr[CountAllocDealloc] x_ptr
+    x_ptr.reset(new CountAllocDealloc(&alloc_count, &dealloc_count))
+    assert alloc_count == 1
+    x_ptr.reset()
+    assert alloc_count == 1
+    assert dealloc_count == 1

tests/run/cpp_smart_ptr_helper.h

+class CountAllocDealloc {
+  public:
+      CountAllocDealloc(int* alloc_count, int* dealloc_count)
+          : _alloc_count(alloc_count), _dealloc_count(dealloc_count) {
+        (*_alloc_count)++;
+      }
+      ~CountAllocDealloc() {
+        (*_dealloc_count)++;
+      }
+  private:
+    int* _alloc_count;
+    int* _dealloc_count;
+};