Draft for new test file

fast_pauli/cpp/tests/test_nb_helpers.cpp

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+/**
+ * This code is part of Fast Pauli.
+ *
+ * (C) Copyright Qognitive Inc 2024.
+ *
+ * This code is licensed under the BSD 2-Clause License. You may
+ * obtain a copy of this license in the LICENSE.txt file in the root directory
+ * of this source tree.
+ *
+ * Any modifications or derivative works of this code must retain this
+ * copyright notice, and modified files need to carry a notice indicating
+ * that they have been altered from the originals.
+ */
+
+#define DOCTEST_CONFIG_IMPLEMENT_WITH_MAIN
+
+#include <doctest/doctest.h>
+
+#include "__nb_helpers.hpp"
+#include "fast_pauli.hpp"
+
+namespace fp = fast_pauli;
+namespace fp_det = fast_pauli::__detail;
+
+TEST_CASE("owning_ndarray_from_mdspan")
+{
+    SUBCASE("single item")
+    {
+        std::vector<float> storage;
+        auto view = fp::zeros<float, 1>(storage, {1});
+        auto ndarray = fp_det::owning_ndarray_from_mdspan<float, 1>(view);
+
+        CHECK(ndarray.size() == 1);
+        CHECK(ndarray.ndim() == 1);
+        CHECK(ndarray.shape(0) == 1);
+    }
+
+    SUBCASE("rank 2")
+    {
+        using complex_t = std::complex<double>;
+
+        std::vector<complex_t> storage;
+        std::mdspan view = fast_pauli::empty<complex_t, 2>(storage, {3, 3});
+        std::iota(storage.begin(), storage.end(), 1);
+        auto ndarray = fp_det::owning_ndarray_from_mdspan<complex_t, 2>(view);
+
+        CHECK(ndarray.size() == 9);
+        CHECK(ndarray.shape(0) == 3);
+        CHECK(ndarray.shape(1) == 3);
+        CHECK(std::equal(storage.begin(), storage.end(), ndarray.data()));
+    }
+}