diff --git a/tests/multi_span_tests.cpp b/tests/multi_span_tests.cpp
new file mode 100644
index 0000000..549dcbe
--- /dev/null
+++ b/tests/multi_span_tests.cpp
@@ -0,0 +1,1701 @@
+///////////////////////////////////////////////////////////////////////////////
+//
+// Copyright (c) 2015 Microsoft Corporation. All rights reserved.
+//
+// This code is licensed under the MIT License (MIT).
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+//
+///////////////////////////////////////////////////////////////////////////////
+
+#include <catch/catch.hpp> // for AssertionHandler, StringRef, CHECK, CHECK...
+
+#include <gsl/gsl_byte>   // for byte
+#include <gsl/gsl_util>   // for narrow_cast
+#include <gsl/multi_span> // for multi_span, contiguous_span_iterator, dim
+
+#include <algorithm> // for fill, for_each
+#include <array>     // for array
+#include <iostream>  // for ptrdiff_t, size_t
+#include <iterator>  // for reverse_iterator, begin, end, operator!=
+#include <numeric>   // for iota
+#include <stddef.h>  // for ptrdiff_t
+#include <string>    // for string
+#include <vector>    // for vector
+
+namespace gsl {
+struct fail_fast;
+}  // namespace gsl
+
+using namespace std;
+using namespace gsl;
+
+namespace
+{
+struct BaseClass
+{
+};
+struct DerivedClass : BaseClass
+{
+};
+}
+
+TEST_CASE("default_constructor")
+{
+    {
+        multi_span<int> s;
+        CHECK((s.length() == 0 && s.data() == nullptr));
+
+        multi_span<const int> cs;
+        CHECK((cs.length() == 0 && cs.data() == nullptr));
+    }
+
+    {
+        multi_span<int, 0> s;
+        CHECK((s.length() == 0 && s.data() == nullptr));
+
+        multi_span<const int, 0> cs;
+        CHECK((cs.length() == 0 && cs.data() == nullptr));
+    }
+
+    {
+#ifdef CONFIRM_COMPILATION_ERRORS
+        multi_span<int, 1> s;
+        CHECK((s.length() == 1 && s.data() == nullptr)); // explains why it can't compile
+#endif
+    }
+
+    {
+        multi_span<int> s{};
+        CHECK((s.length() == 0 && s.data() == nullptr));
+
+        multi_span<const int> cs{};
+        CHECK((cs.length() == 0 && cs.data() == nullptr));
+    }
+}
+
+TEST_CASE("from_nullptr_constructor")
+{
+    {
+        multi_span<int> s = nullptr;
+        CHECK((s.length() == 0 && s.data() == nullptr));
+
+        multi_span<const int> cs = nullptr;
+        CHECK((cs.length() == 0 && cs.data() == nullptr));
+    }
+
+    {
+        multi_span<int, 0> s = nullptr;
+        CHECK((s.length() == 0 && s.data() == nullptr));
+
+        multi_span<const int, 0> cs = nullptr;
+        CHECK((cs.length() == 0 && cs.data() == nullptr));
+    }
+
+    {
+#ifdef CONFIRM_COMPILATION_ERRORS
+        multi_span<int, 1> s = nullptr;
+        CHECK((s.length() == 1 && s.data() == nullptr)); // explains why it can't compile
+#endif
+    }
+
+    {
+        multi_span<int> s{nullptr};
+        CHECK((s.length() == 0 && s.data() == nullptr));
+
+        multi_span<const int> cs{nullptr};
+        CHECK((cs.length() == 0 && cs.data() == nullptr));
+    }
+
+    {
+        multi_span<int*> s{nullptr};
+        CHECK((s.length() == 0 && s.data() == nullptr));
+
+        multi_span<const int*> cs{nullptr};
+        CHECK((cs.length() == 0 && cs.data() == nullptr));
+    }
+}
+
+TEST_CASE("from_nullptr_length_constructor")
+{
+    {
+        multi_span<int> s{nullptr, 0};
+        CHECK((s.length() == 0 && s.data() == nullptr));
+
+        multi_span<const int> cs{nullptr, 0};
+        CHECK((cs.length() == 0 && cs.data() == nullptr));
+    }
+
+    {
+        multi_span<int, 0> s{nullptr, 0};
+        CHECK((s.length() == 0 && s.data() == nullptr));
+
+        multi_span<const int, 0> cs{nullptr, 0};
+        CHECK((cs.length() == 0 && cs.data() == nullptr));
+    }
+
+    {
+#ifdef CONFIRM_COMPILATION_ERRORS
+        multi_span<int, 1> s{nullptr, 0};
+        CHECK((s.length() == 1 && s.data() == nullptr)); // explains why it can't compile
+#endif
+    }
+
+    {
+        auto workaround_macro = []() { multi_span<int> s{nullptr, 1}; };
+        CHECK_THROWS_AS(workaround_macro(), fail_fast);
+
+        auto const_workaround_macro = []() { multi_span<const int> cs{nullptr, 1}; };
+        CHECK_THROWS_AS(const_workaround_macro(), fail_fast);
+    }
+
+    {
+        auto workaround_macro = []() { multi_span<int, 0> s{nullptr, 1}; };
+        CHECK_THROWS_AS(workaround_macro(), fail_fast);
+
+        auto const_workaround_macro = []() { multi_span<const int, 0> s{nullptr, 1}; };
+        CHECK_THROWS_AS(const_workaround_macro(), fail_fast);
+    }
+
+    {
+        multi_span<int*> s{nullptr, 0};
+        CHECK((s.length() == 0 && s.data() == nullptr));
+
+        multi_span<const int*> cs{nullptr, 0};
+        CHECK((cs.length() == 0 && cs.data() == nullptr));
+    }
+}
+
+TEST_CASE("from_element_constructor")
+{
+    int i = 5;
+
+    {
+        multi_span<int> s = i;
+        CHECK((s.length() == 1 && s.data() == &i));
+        CHECK(s[0] == 5);
+
+        multi_span<const int> cs = i;
+        CHECK((cs.length() == 1 && cs.data() == &i));
+        CHECK(cs[0] == 5);
+    }
+
+    {
+#ifdef CONFIRM_COMPILATION_ERRORS
+        const j = 1;
+        multi_span<int, 0> s = j;
+#endif
+    }
+
+    {
+#ifdef CONFIRM_COMPILATION_ERRORS
+        multi_span<int, 0> s = i;
+        CHECK((s.length() == 0 && s.data() == &i));
+#endif
+    }
+
+    {
+        multi_span<int, 1> s = i;
+        CHECK((s.length() == 1 && s.data() == &i));
+        CHECK(s[0] == 5);
+    }
+
+    {
+#ifdef CONFIRM_COMPILATION_ERRORS
+        multi_span<int, 2> s = i;
+        CHECK((s.length() == 2 && s.data() == &i));
+#endif
+    }
+
+    {
+#ifdef CONFIRM_COMPILATION_ERRORS
+        auto get_a_temp = []() -> int { return 4; };
+        auto use_a_span = [](multi_span<int> s) { (void) s; };
+        use_a_span(get_a_temp());
+#endif
+    }
+}
+
+TEST_CASE("from_pointer_length_constructor")
+{
+    int arr[4] = {1, 2, 3, 4};
+
+    {
+        multi_span<int> s{&arr[0], 2};
+        CHECK((s.length() == 2 && s.data() == &arr[0]));
+        CHECK((s[0] == 1 && s[1] == 2));
+    }
+
+    {
+        multi_span<int, 2> s{&arr[0], 2};
+        CHECK((s.length() == 2 && s.data() == &arr[0]));
+        CHECK((s[0] == 1 && s[1] == 2));
+    }
+
+    {
+        int* p = nullptr;
+        multi_span<int> s{p, 0};
+        CHECK((s.length() == 0 && s.data() == nullptr));
+    }
+
+    {
+        int* p = nullptr;
+        auto workaround_macro = [=]() { multi_span<int> s{p, 2}; };
+        CHECK_THROWS_AS(workaround_macro(), fail_fast);
+    }
+}
+
+TEST_CASE("from_pointer_pointer_constructor")
+{
+    int arr[4] = {1, 2, 3, 4};
+
+    {
+        multi_span<int> s{&arr[0], &arr[2]};
+        CHECK((s.length() == 2 && s.data() == &arr[0]));
+        CHECK((s[0] == 1 && s[1] == 2));
+    }
+
+    {
+        multi_span<int, 2> s{&arr[0], &arr[2]};
+        CHECK((s.length() == 2 && s.data() == &arr[0]));
+        CHECK((s[0] == 1 && s[1] == 2));
+    }
+
+    {
+        multi_span<int> s{&arr[0], &arr[0]};
+        CHECK((s.length() == 0 && s.data() == &arr[0]));
+    }
+
+    {
+        multi_span<int, 0> s{&arr[0], &arr[0]};
+        CHECK((s.length() == 0 && s.data() == &arr[0]));
+    }
+
+    {
+        auto workaround_macro = [&]() { multi_span<int> s{&arr[1], &arr[0]}; };
+        CHECK_THROWS_AS(workaround_macro(), fail_fast);
+    }
+
+    {
+        int* p = nullptr;
+        auto workaround_macro = [&]() { multi_span<int> s{&arr[0], p}; };
+        CHECK_THROWS_AS(workaround_macro(), fail_fast);
+    }
+
+    {
+        int* p = nullptr;
+        auto workaround_macro = [&]() { multi_span<int> s{p, p}; };
+        CHECK_THROWS_AS(workaround_macro(), fail_fast);
+    }
+
+    {
+        int* p = nullptr;
+        auto workaround_macro = [&]() { multi_span<int> s{&arr[0], p}; };
+        CHECK_THROWS_AS(workaround_macro(), fail_fast);
+    }
+}
+
+TEST_CASE("from_array_constructor")
+{
+    int arr[5] = {1, 2, 3, 4, 5};
+
+    {
+        multi_span<int> s{arr};
+        CHECK((s.length() == 5 && s.data() == &arr[0]));
+    }
+
+    {
+        multi_span<int, 5> s{arr};
+        CHECK((s.length() == 5 && s.data() == &arr[0]));
+    }
+
+    {
+#ifdef CONFIRM_COMPILATION_ERRORS
+        multi_span<int, 6> s{arr};
+#endif
+    }
+
+    {
+        multi_span<int, 0> s{arr};
+        CHECK((s.length() == 0 && s.data() == &arr[0]));
+    }
+
+    int arr2d[2][3] = {1, 2, 3, 4, 5, 6};
+
+    {
+        multi_span<int> s{arr2d};
+        CHECK((s.length() == 6 && s.data() == &arr2d[0][0]));
+        CHECK((s[0] == 1 && s[5] == 6));
+    }
+
+    {
+        multi_span<int, 0> s{arr2d};
+        CHECK((s.length() == 0 && s.data() == &arr2d[0][0]));
+    }
+
+    {
+#ifdef CONFIRM_COMPILATION_ERRORS
+        multi_span<int, 5> s{arr2d};
+#endif
+    }
+
+    {
+        multi_span<int, 6> s{arr2d};
+        CHECK((s.length() == 6 && s.data() == &arr2d[0][0]));
+        CHECK((s[0] == 1 && s[5] == 6));
+    }
+
+    {
+#ifdef CONFIRM_COMPILATION_ERRORS
+        multi_span<int, 7> s{arr2d};
+#endif
+    }
+
+    {
+        multi_span<int[3]> s{arr2d[0]};
+        CHECK((s.length() == 1 && s.data() == &arr2d[0]));
+    }
+
+    {
+        multi_span<int, 2, 3> s{arr2d};
+        CHECK((s.length() == 6 && s.data() == &arr2d[0][0]));
+        auto workaround_macro = [&]() { return s[{1, 2}] == 6; };
+        CHECK(workaround_macro());
+    }
+
+    {
+#ifdef CONFIRM_COMPILATION_ERRORS
+        multi_span<int, 3, 3> s{arr2d};
+#endif
+    }
+
+    int arr3d[2][3][2] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12};
+
+    {
+        multi_span<int> s{arr3d};
+        CHECK((s.length() == 12 && s.data() == &arr3d[0][0][0]));
+        CHECK((s[0] == 1 && s[11] == 12));
+    }
+
+    {
+        multi_span<int, 0> s{arr3d};
+        CHECK((s.length() == 0 && s.data() == &arr3d[0][0][0]));
+    }
+
+    {
+#ifdef CONFIRM_COMPILATION_ERRORS
+        multi_span<int, 11> s{arr3d};
+#endif
+    }
+
+    {
+        multi_span<int, 12> s{arr3d};
+        CHECK((s.length() == 12 && s.data() == &arr3d[0][0][0]));
+        CHECK((s[0] == 1 && s[5] == 6));
+    }
+
+    {
+#ifdef CONFIRM_COMPILATION_ERRORS
+        multi_span<int, 13> s{arr3d};
+#endif
+    }
+
+    {
+        multi_span<int[3][2]> s{arr3d[0]};
+        CHECK((s.length() == 1 && s.data() == &arr3d[0]));
+    }
+
+    {
+        multi_span<int, 3, 2, 2> s{arr3d};
+        CHECK((s.length() == 12 && s.data() == &arr3d[0][0][0]));
+        auto workaround_macro = [&]() { return s[{2, 1, 0}] == 11; };
+        CHECK(workaround_macro());
+    }
+
+    {
+#ifdef CONFIRM_COMPILATION_ERRORS
+        multi_span<int, 3, 3, 3> s{arr3d};
+#endif
+    }
+}
+
+TEST_CASE("from_dynamic_array_constructor")
+{
+    double(*arr)[3][4] = new double[100][3][4];
+
+    {
+        multi_span<double, dynamic_range, 3, 4> s(arr, 10);
+        CHECK((s.length() == 120 && s.data() == &arr[0][0][0]));
+        CHECK_THROWS_AS(s[10][3][4], fail_fast);
+    }
+
+    {
+        multi_span<double, dynamic_range, 4, 3> s(arr, 10);
+        CHECK((s.length() == 120 && s.data() == &arr[0][0][0]));
+    }
+
+    {
+        multi_span<double> s(arr, 10);
+        CHECK((s.length() == 120 && s.data() == &arr[0][0][0]));
+    }
+
+    {
+        multi_span<double, dynamic_range, 3, 4> s(arr, 0);
+        CHECK((s.length() == 0 && s.data() == &arr[0][0][0]));
+    }
+
+    delete[] arr;
+}
+
+TEST_CASE("from_std_array_constructor")
+{
+    std::array<int, 4> arr = {1, 2, 3, 4};
+
+    {
+        multi_span<int> s{arr};
+        CHECK((s.size() == narrow_cast<ptrdiff_t>(arr.size()) && s.data() == arr.data()));
+
+        multi_span<const int> cs{arr};
+        CHECK((cs.size() == narrow_cast<ptrdiff_t>(arr.size()) && cs.data() == arr.data()));
+    }
+
+    {
+        multi_span<int, 4> s{arr};
+        CHECK((s.size() == narrow_cast<ptrdiff_t>(arr.size()) && s.data() == arr.data()));
+
+        multi_span<const int, 4> cs{arr};
+        CHECK((cs.size() == narrow_cast<ptrdiff_t>(arr.size()) && cs.data() == arr.data()));
+    }
+
+    {
+        multi_span<int, 2> s{arr};
+        CHECK((s.size() == 2 && s.data() == arr.data()));
+
+        multi_span<const int, 2> cs{arr};
+        CHECK((cs.size() == 2 && cs.data() == arr.data()));
+    }
+
+    {
+        multi_span<int, 0> s{arr};
+        CHECK((s.size() == 0 && s.data() == arr.data()));
+
+        multi_span<const int, 0> cs{arr};
+        CHECK((cs.size() == 0 && cs.data() == arr.data()));
+    }
+
+    // TODO This is currently an unsupported scenario. We will come back to it as we revise
+    // the multidimensional interface and what transformations between dimensionality look like
+    //{
+    //    multi_span<int, 2, 2> s{arr};
+    //    CHECK(s.size() == narrow_cast<ptrdiff_t>(arr.size()) && s.data() == arr.data());
+    //}
+
+    {
+#ifdef CONFIRM_COMPILATION_ERRORS
+        multi_span<int, 5> s{arr};
+#endif
+    }
+
+    {
+#ifdef CONFIRM_COMPILATION_ERRORS
+        auto get_an_array = []() { return std::array<int, 4>{1, 2, 3, 4}; };
+        auto take_a_span = [](multi_span<int> s) { (void) s; };
+        // try to take a temporary std::array
+        take_a_span(get_an_array());
+#endif
+    }
+}
+
+TEST_CASE("from_const_std_array_constructor")
+{
+    const std::array<int, 4> arr = {1, 2, 3, 4};
+
+    {
+        multi_span<const int> s{arr};
+        CHECK((s.size() == narrow_cast<ptrdiff_t>(arr.size()) && s.data() == arr.data()));
+    }
+
+    {
+        multi_span<const int, 4> s{arr};
+        CHECK((s.size() == narrow_cast<ptrdiff_t>(arr.size()) && s.data() == arr.data()));
+    }
+
+    {
+        multi_span<const int, 2> s{arr};
+        CHECK((s.size() == 2 && s.data() == arr.data()));
+    }
+
+    {
+        multi_span<const int, 0> s{arr};
+        CHECK((s.size() == 0 && s.data() == arr.data()));
+    }
+
+    // TODO This is currently an unsupported scenario. We will come back to it as we revise
+    // the multidimensional interface and what transformations between dimensionality look like
+    //{
+    //    multi_span<int, 2, 2> s{arr};
+    //    CHECK(s.size() == narrow_cast<ptrdiff_t>(arr.size()) && s.data() == arr.data());
+    //}
+
+    {
+#ifdef CONFIRM_COMPILATION_ERRORS
+        multi_span<const int, 5> s{arr};
+#endif
+    }
+
+    {
+#ifdef CONFIRM_COMPILATION_ERRORS
+        auto get_an_array = []() -> const std::array<int, 4> { return {1, 2, 3, 4}; };
+        auto take_a_span = [](multi_span<const int> s) { (void) s; };
+        // try to take a temporary std::array
+        take_a_span(get_an_array());
+#endif
+    }
+}
+
+TEST_CASE("from_container_constructor")
+{
+    std::vector<int> v = {1, 2, 3};
+    const std::vector<int> cv = v;
+
+    {
+        multi_span<int> s{v};
+        CHECK((s.size() == narrow_cast<std::ptrdiff_t>(v.size()) && s.data() == v.data()));
+
+        multi_span<const int> cs{v};
+        CHECK((cs.size() == narrow_cast<std::ptrdiff_t>(v.size()) && cs.data() == v.data()));
+    }
+
+    std::string str = "hello";
+    const std::string cstr = "hello";
+
+    {
+#ifdef CONFIRM_COMPILATION_ERRORS
+        multi_span<char> s{str};
+        CHECK((s.size() == narrow_cast<std::ptrdiff_t>(str.size()) && s.data() == str.data()));
+#endif
+        multi_span<const char> cs{str};
+        CHECK((cs.size() == narrow_cast<std::ptrdiff_t>(str.size()) && cs.data() == str.data()));
+    }
+
+    {
+#ifdef CONFIRM_COMPILATION_ERRORS
+        multi_span<char> s{cstr};
+#endif
+        multi_span<const char> cs{cstr};
+        CHECK((cs.size() == narrow_cast<std::ptrdiff_t>(cstr.size()) &&
+               cs.data() == cstr.data()));
+    }
+
+    {
+#ifdef CONFIRM_COMPILATION_ERRORS
+        auto get_temp_vector = []() -> std::vector<int> { return {}; };
+        auto use_span = [](multi_span<int> s) { (void) s; };
+        use_span(get_temp_vector());
+#endif
+    }
+
+    {
+#ifdef CONFIRM_COMPILATION_ERRORS
+        auto get_temp_string = []() -> std::string { return {}; };
+        auto use_span = [](multi_span<char> s) { (void) s; };
+        use_span(get_temp_string());
+#endif
+    }
+
+    {
+#ifdef CONFIRM_COMPILATION_ERRORS
+        auto get_temp_vector = []() -> const std::vector<int> { return {}; };
+        auto use_span = [](multi_span<const char> s) { (void) s; };
+        use_span(get_temp_vector());
+#endif
+    }
+
+    {
+#ifdef CONFIRM_COMPILATION_ERRORS
+        auto get_temp_string = []() -> const std::string { return {}; };
+        auto use_span = [](multi_span<const char> s) { (void) s; };
+        use_span(get_temp_string());
+#endif
+    }
+
+    {
+#ifdef CONFIRM_COMPILATION_ERRORS
+        std::map<int, int> m;
+        multi_span<int> s{m};
+#endif
+    }
+}
+
+TEST_CASE("from_convertible_span_constructor")
+{
+#ifdef CONFIRM_COMPILATION_ERRORS
+    multi_span<int, 7, 4, 2> av1(nullptr, b1);
+
+    auto f = [&]() { multi_span<int, 7, 4, 2> av1(nullptr); };
+    CHECK_THROWS_AS(f(), fail_fast);
+#endif
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+    static_bounds<std::size_t, 7, dynamic_range, 2> b12(b11);
+    b12 = b11;
+    b11 = b12;
+
+    multi_span<int, dynamic_range> av1 = nullptr;
+    multi_span<int, 7, dynamic_range, 2> av2(av1);
+    multi_span<int, 7, 4, 2> av2(av1);
+#endif
+
+    multi_span<DerivedClass> avd;
+#ifdef CONFIRM_COMPILATION_ERRORS
+    multi_span<BaseClass> avb = avd;
+#endif
+    multi_span<const DerivedClass> avcd = avd;
+    (void) avcd;
+}
+
+TEST_CASE("copy_move_and_assignment")
+{
+    multi_span<int> s1;
+    CHECK(s1.empty());
+
+    int arr[] = {3, 4, 5};
+
+    multi_span<const int> s2 = arr;
+    CHECK((s2.length() == 3 && s2.data() == &arr[0]));
+
+    s2 = s1;
+    CHECK(s2.empty());
+
+    auto get_temp_span = [&]() -> multi_span<int> { return {&arr[1], 2}; };
+    auto use_span = [&](multi_span<const int> s) {
+        CHECK((s.length() == 2 && s.data() == &arr[1]));
+    };
+    use_span(get_temp_span());
+
+    s1 = get_temp_span();
+    CHECK((s1.length() == 2 && s1.data() == &arr[1]));
+}
+
+template <class Bounds>
+void fn(const Bounds&)
+{
+    static_assert(Bounds::static_size == 60, "static bounds is wrong size");
+}
+TEST_CASE("as_multi_span_reshape")
+{
+    int a[3][4][5];
+    auto av = as_multi_span(a);
+    fn(av.bounds());
+    auto av2 = as_multi_span(av, dim<60>());
+    auto av3 = as_multi_span(av2, dim<3>(), dim<4>(), dim<5>());
+    auto av4 = as_multi_span(av3, dim<4>(), dim(3), dim<5>());
+    auto av5 = as_multi_span(av4, dim<3>(), dim<4>(), dim<5>());
+    auto av6 = as_multi_span(av5, dim<12>(), dim(5));
+
+    fill(av6.begin(), av6.end(), 1);
+
+    auto av7 = as_bytes(av6);
+
+    auto av8 = as_multi_span<int>(av7);
+
+    CHECK(av8.size() == av6.size());
+    for (auto i = 0; i < av8.size(); i++) {
+        CHECK(av8[i] == 1);
+    }
+}
+
+TEST_CASE("first")
+{
+    int arr[5] = {1, 2, 3, 4, 5};
+
+    {
+        multi_span<int, 5> av = arr;
+        CHECK((av.first<2>().bounds() == static_bounds<2>()));
+        CHECK(av.first<2>().length() == 2);
+        CHECK(av.first(2).length() == 2);
+    }
+
+    {
+        multi_span<int, 5> av = arr;
+        CHECK((av.first<0>().bounds() == static_bounds<0>()));
+        CHECK(av.first<0>().length() == 0);
+        CHECK(av.first(0).length() == 0);
+    }
+
+    {
+        multi_span<int, 5> av = arr;
+        CHECK((av.first<5>().bounds() == static_bounds<5>()));
+        CHECK(av.first<5>().length() == 5);
+        CHECK(av.first(5).length() == 5);
+    }
+
+    {
+        multi_span<int, 5> av = arr;
+#ifdef CONFIRM_COMPILATION_ERRORS
+        CHECK(av.first<6>().bounds() == static_bounds<6>());
+        CHECK(av.first<6>().length() == 6);
+        CHECK(av.first<-1>().length() == -1);
+#endif
+        CHECK_THROWS_AS(av.first(6).length(), fail_fast);
+    }
+
+    {
+        multi_span<int, dynamic_range> av;
+        CHECK((av.first<0>().bounds() == static_bounds<0>()));
+        CHECK(av.first<0>().length() == 0);
+        CHECK(av.first(0).length() == 0);
+    }
+}
+
+TEST_CASE("last")
+{
+    int arr[5] = {1, 2, 3, 4, 5};
+
+    {
+        multi_span<int, 5> av = arr;
+        CHECK((av.last<2>().bounds() == static_bounds<2>()));
+        CHECK(av.last<2>().length() == 2);
+        CHECK(av.last(2).length() == 2);
+    }
+
+    {
+        multi_span<int, 5> av = arr;
+        CHECK((av.last<0>().bounds() == static_bounds<0>()));
+        CHECK(av.last<0>().length() == 0);
+        CHECK(av.last(0).length() == 0);
+    }
+
+    {
+        multi_span<int, 5> av = arr;
+        CHECK((av.last<5>().bounds() == static_bounds<5>()));
+        CHECK(av.last<5>().length() == 5);
+        CHECK(av.last(5).length() == 5);
+    }
+
+    {
+        multi_span<int, 5> av = arr;
+#ifdef CONFIRM_COMPILATION_ERRORS
+        CHECK((av.last<6>().bounds() == static_bounds<6>()));
+        CHECK(av.last<6>().length() == 6);
+#endif
+        CHECK_THROWS_AS(av.last(6).length(), fail_fast);
+    }
+
+    {
+        multi_span<int, dynamic_range> av;
+        CHECK((av.last<0>().bounds() == static_bounds<0>()));
+        CHECK(av.last<0>().length() == 0);
+        CHECK(av.last(0).length() == 0);
+    }
+}
+
+TEST_CASE("subspan")
+{
+    int arr[5] = {1, 2, 3, 4, 5};
+
+    {
+        multi_span<int, 5> av = arr;
+        CHECK((av.subspan<2, 2>().bounds() == static_bounds<2>()));
+        CHECK((av.subspan<2, 2>().length() == 2));
+        CHECK(av.subspan(2, 2).length() == 2);
+        CHECK(av.subspan(2, 3).length() == 3);
+    }
+
+    {
+        multi_span<int, 5> av = arr;
+        CHECK((av.subspan<0, 0>().bounds() == static_bounds<0>()));
+        CHECK((av.subspan<0, 0>().length() == 0));
+        CHECK(av.subspan(0, 0).length() == 0);
+    }
+
+    {
+        multi_span<int, 5> av = arr;
+        CHECK((av.subspan<0, 5>().bounds() == static_bounds<5>()));
+        CHECK((av.subspan<0, 5>().length() == 5));
+        CHECK(av.subspan(0, 5).length() == 5);
+        CHECK_THROWS_AS(av.subspan(0, 6).length(), fail_fast);
+        CHECK_THROWS_AS(av.subspan(1, 5).length(), fail_fast);
+    }
+
+    {
+        multi_span<int, 5> av = arr;
+        CHECK((av.subspan<5, 0>().bounds() == static_bounds<0>()));
+        CHECK((av.subspan<5, 0>().length() == 0));
+        CHECK(av.subspan(5, 0).length() == 0);
+        CHECK_THROWS_AS(av.subspan(6, 0).length(), fail_fast);
+    }
+
+    {
+        multi_span<int, dynamic_range> av;
+        CHECK((av.subspan<0, 0>().bounds() == static_bounds<0>()));
+        CHECK((av.subspan<0, 0>().length() == 0));
+        CHECK(av.subspan(0, 0).length() == 0);
+        CHECK_THROWS_AS((av.subspan<1, 0>().length()), fail_fast);
+    }
+
+    {
+        multi_span<int> av;
+        CHECK(av.subspan(0).length() == 0);
+        CHECK_THROWS_AS(av.subspan(1).length(), fail_fast);
+    }
+
+    {
+        multi_span<int> av = arr;
+        CHECK(av.subspan(0).length() == 5);
+        CHECK(av.subspan(1).length() == 4);
+        CHECK(av.subspan(4).length() == 1);
+        CHECK(av.subspan(5).length() == 0);
+        CHECK_THROWS_AS(av.subspan(6).length(), fail_fast);
+        auto av2 = av.subspan(1);
+        for (int i = 0; i < 4; ++i) CHECK(av2[i] == i + 2);
+    }
+
+    {
+        multi_span<int, 5> av = arr;
+        CHECK(av.subspan(0).length() == 5);
+        CHECK(av.subspan(1).length() == 4);
+        CHECK(av.subspan(4).length() == 1);
+        CHECK(av.subspan(5).length() == 0);
+        CHECK_THROWS_AS(av.subspan(6).length(), fail_fast);
+        auto av2 = av.subspan(1);
+        for (int i = 0; i < 4; ++i) CHECK(av2[i] == i + 2);
+    }
+}
+
+TEST_CASE("rank")
+{
+    int arr[2] = {1, 2};
+
+    {
+        multi_span<int> s;
+        CHECK(s.rank() == 1);
+    }
+
+    {
+        multi_span<int, 2> s = arr;
+        CHECK(s.rank() == 1);
+    }
+
+    int arr2d[1][1] = {};
+    {
+        multi_span<int, 1, 1> s = arr2d;
+        CHECK(s.rank() == 2);
+    }
+}
+
+TEST_CASE("extent")
+{
+    {
+        multi_span<int> s;
+        CHECK(s.extent() == 0);
+        CHECK(s.extent(0) == 0);
+        CHECK_THROWS_AS(s.extent(1), fail_fast);
+#ifdef CONFIRM_COMPILATION_ERRORS
+        CHECK(s.extent<1>() == 0);
+#endif
+    }
+
+    {
+        multi_span<int, 0> s;
+        CHECK(s.extent() == 0);
+        CHECK(s.extent(0) == 0);
+        CHECK_THROWS_AS(s.extent(1), fail_fast);
+    }
+
+    {
+        int arr2d[1][2] = {};
+
+        multi_span<int, 1, 2> s = arr2d;
+        CHECK(s.extent() == 1);
+        CHECK(s.extent<0>() == 1);
+        CHECK(s.extent<1>() == 2);
+        CHECK(s.extent(0) == 1);
+        CHECK(s.extent(1) == 2);
+        CHECK_THROWS_AS(s.extent(3), fail_fast);
+    }
+
+    {
+        int arr2d[1][2] = {};
+
+        multi_span<int, 0, 2> s = arr2d;
+        CHECK(s.extent() == 0);
+        CHECK(s.extent<0>() == 0);
+        CHECK(s.extent<1>() == 2);
+        CHECK(s.extent(0) == 0);
+        CHECK(s.extent(1) == 2);
+        CHECK_THROWS_AS(s.extent(3), fail_fast);
+    }
+}
+
+TEST_CASE("operator_function_call")
+{
+    int arr[4] = {1, 2, 3, 4};
+
+    {
+        multi_span<int> s = arr;
+        CHECK(s(0) == 1);
+        CHECK_THROWS_AS(s(5), fail_fast);
+    }
+
+    int arr2d[2][3] = {1, 2, 3, 4, 5, 6};
+
+    {
+        multi_span<int, 2, 3> s = arr2d;
+        CHECK(s(0, 0) == 1);
+        CHECK(s(0, 1) == 2);
+        CHECK(s(1, 2) == 6);
+    }
+
+    int arr3d[2][2][2] = {1, 2, 3, 4, 5, 6, 7, 8};
+
+    {
+        multi_span<int, 2, 2, 2> s = arr3d;
+        CHECK(s(0, 0, 0) == 1);
+        CHECK(s(1, 1, 1) == 8);
+    }
+}
+
+TEST_CASE("comparison_operators")
+{
+    {
+        int arr[10][2];
+        auto s1 = as_multi_span(arr);
+        multi_span<const int, dynamic_range, 2> s2 = s1;
+
+        CHECK(s1 == s2);
+
+        multi_span<int, 20> s3 = as_multi_span(s1, dim(20));
+        CHECK((s3 == s2 && s3 == s1));
+    }
+
+    {
+        multi_span<int> s1 = nullptr;
+        multi_span<int> s2 = nullptr;
+        CHECK(s1 == s2);
+        CHECK(!(s1 != s2));
+        CHECK(!(s1 < s2));
+        CHECK(s1 <= s2);
+        CHECK(!(s1 > s2));
+        CHECK(s1 >= s2);
+        CHECK(s2 == s1);
+        CHECK(!(s2 != s1));
+        CHECK(!(s2 < s1));
+        CHECK(s2 <= s1);
+        CHECK(!(s2 > s1));
+        CHECK(s2 >= s1);
+    }
+
+    {
+        int arr[] = {2, 1}; // bigger
+
+        multi_span<int> s1 = nullptr;
+        multi_span<int> s2 = arr;
+
+        CHECK(s1 != s2);
+        CHECK(s2 != s1);
+        CHECK(!(s1 == s2));
+        CHECK(!(s2 == s1));
+        CHECK(s1 < s2);
+        CHECK(!(s2 < s1));
+        CHECK(s1 <= s2);
+        CHECK(!(s2 <= s1));
+        CHECK(s2 > s1);
+        CHECK(!(s1 > s2));
+        CHECK(s2 >= s1);
+        CHECK(!(s1 >= s2));
+    }
+
+    {
+        int arr1[] = {1, 2};
+        int arr2[] = {1, 2};
+        multi_span<int> s1 = arr1;
+        multi_span<int> s2 = arr2;
+
+        CHECK(s1 == s2);
+        CHECK(!(s1 != s2));
+        CHECK(!(s1 < s2));
+        CHECK(s1 <= s2);
+        CHECK(!(s1 > s2));
+        CHECK(s1 >= s2);
+        CHECK(s2 == s1);
+        CHECK(!(s2 != s1));
+        CHECK(!(s2 < s1));
+        CHECK(s2 <= s1);
+        CHECK(!(s2 > s1));
+        CHECK(s2 >= s1);
+    }
+
+    {
+        int arr[] = {1, 2, 3};
+
+        multi_span<int> s1 = {&arr[0], 2}; // shorter
+        multi_span<int> s2 = arr;          // longer
+
+        CHECK(s1 != s2);
+        CHECK(s2 != s1);
+        CHECK(!(s1 == s2));
+        CHECK(!(s2 == s1));
+        CHECK(s1 < s2);
+        CHECK(!(s2 < s1));
+        CHECK(s1 <= s2);
+        CHECK(!(s2 <= s1));
+        CHECK(s2 > s1);
+        CHECK(!(s1 > s2));
+        CHECK(s2 >= s1);
+        CHECK(!(s1 >= s2));
+    }
+
+    {
+        int arr1[] = {1, 2}; // smaller
+        int arr2[] = {2, 1}; // bigger
+
+        multi_span<int> s1 = arr1;
+        multi_span<int> s2 = arr2;
+
+        CHECK(s1 != s2);
+        CHECK(s2 != s1);
+        CHECK(!(s1 == s2));
+        CHECK(!(s2 == s1));
+        CHECK(s1 < s2);
+        CHECK(!(s2 < s1));
+        CHECK(s1 <= s2);
+        CHECK(!(s2 <= s1));
+        CHECK(s2 > s1);
+        CHECK(!(s1 > s2));
+        CHECK(s2 >= s1);
+        CHECK(!(s1 >= s2));
+    }
+}
+
+TEST_CASE("basics")
+{
+    auto ptr = as_multi_span(new int[10], 10);
+    fill(ptr.begin(), ptr.end(), 99);
+    for (int num : ptr) {
+        CHECK(num == 99);
+    }
+
+    delete[] ptr.data();
+}
+
+TEST_CASE("bounds_checks")
+{
+    int arr[10][2];
+    auto av = as_multi_span(arr);
+
+    fill(begin(av), end(av), 0);
+
+    av[2][0] = 1;
+    av[1][1] = 3;
+
+    // out of bounds
+    CHECK_THROWS_AS(av[1][3] = 3, fail_fast);
+    CHECK_THROWS_AS((av[{1, 3}] = 3), fail_fast);
+
+    CHECK_THROWS_AS(av[10][2], fail_fast);
+    CHECK_THROWS_AS((av[{10, 2}]), fail_fast);
+
+    CHECK_THROWS_AS(av[-1][0], fail_fast);
+    CHECK_THROWS_AS((av[{-1, 0}]), fail_fast);
+
+    CHECK_THROWS_AS(av[0][-1], fail_fast);
+    CHECK_THROWS_AS((av[{0, -1}]), fail_fast);
+}
+
+void overloaded_func(multi_span<const int, dynamic_range, 3, 5> exp, int expected_value)
+{
+    for (auto val : exp) {
+        CHECK(val == expected_value);
+    }
+}
+
+void overloaded_func(multi_span<const char, dynamic_range, 3, 5> exp, char expected_value)
+{
+    for (auto val : exp) {
+        CHECK(val == expected_value);
+    }
+}
+
+void fixed_func(multi_span<int, 3, 3, 5> exp, int expected_value)
+{
+    for (auto val : exp) {
+        CHECK(val == expected_value);
+    }
+}
+
+TEST_CASE("span_parameter_test")
+{
+    auto data = new int[4][3][5];
+
+    auto av = as_multi_span(data, 4);
+
+    CHECK(av.size() == 60);
+
+    fill(av.begin(), av.end(), 34);
+
+    int count = 0;
+    for_each(av.rbegin(), av.rend(), [&](int val) { count += val; });
+    CHECK(count == 34 * 60);
+    overloaded_func(av, 34);
+
+    overloaded_func(as_multi_span(av, dim(4), dim(3), dim(5)), 34);
+
+    // fixed_func(av, 34);
+    delete[] data;
+}
+
+TEST_CASE("md_access")
+{
+    auto width = 5, height = 20;
+
+    auto imgSize = width * height;
+    auto image_ptr = new int[static_cast<std::size_t>(imgSize)][3];
+
+    // size check will be done
+    auto image_view =
+        as_multi_span(as_multi_span(image_ptr, imgSize), dim(height), dim(width), dim<3>());
+
+    iota(image_view.begin(), image_view.end(), 1);
+
+    int expected = 0;
+    for (auto i = 0; i < height; i++) {
+        for (auto j = 0; j < width; j++) {
+            CHECK(expected + 1 == image_view[i][j][0]);
+            CHECK(expected + 2 == image_view[i][j][1]);
+            CHECK(expected + 3 == image_view[i][j][2]);
+
+            auto val = image_view[{i, j, 0}];
+            CHECK(expected + 1 == val);
+            val = image_view[{i, j, 1}];
+            CHECK(expected + 2 == val);
+            val = image_view[{i, j, 2}];
+            CHECK(expected + 3 == val);
+
+            expected += 3;
+        }
+    }
+}
+
+TEST_CASE("as_multi_span")
+{
+    {
+        int* arr = new int[150];
+
+        auto av = as_multi_span(arr, dim<10>(), dim(3), dim<5>());
+
+        fill(av.begin(), av.end(), 24);
+        overloaded_func(av, 24);
+
+        delete[] arr;
+
+        array<int, 15> stdarr{0};
+        auto av2 = as_multi_span(stdarr);
+        overloaded_func(as_multi_span(av2, dim(1), dim<3>(), dim<5>()), 0);
+
+        string str = "ttttttttttttttt"; // size = 15
+        auto t = str.data();
+        (void) t;
+        auto av3 = as_multi_span(str);
+        overloaded_func(as_multi_span(av3, dim(1), dim<3>(), dim<5>()), 't');
+    }
+
+    {
+        string str;
+        multi_span<char> strspan = as_multi_span(str);
+        (void) strspan;
+        const string cstr;
+        multi_span<const char> cstrspan = as_multi_span(cstr);
+        (void) cstrspan;
+    }
+
+    {
+        int a[3][4][5];
+        auto av = as_multi_span(a);
+        const int(*b)[4][5];
+        b = a;
+        auto bv = as_multi_span(b, 3);
+
+        CHECK(av == bv);
+
+        const std::array<double, 3> arr = {0.0, 0.0, 0.0};
+        auto cv = as_multi_span(arr);
+        (void) cv;
+
+        vector<float> vec(3);
+        auto dv = as_multi_span(vec);
+        (void) dv;
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+        auto dv2 = as_multi_span(std::move(vec));
+#endif
+    }
+}
+
+TEST_CASE("empty_spans")
+{
+    {
+        multi_span<int, 0> empty_av(nullptr);
+
+        CHECK(empty_av.bounds().index_bounds() == multi_span_index<1>{0});
+        CHECK_THROWS_AS(empty_av[0], fail_fast);
+        CHECK_THROWS_AS(empty_av.begin()[0], fail_fast);
+        CHECK_THROWS_AS(empty_av.cbegin()[0], fail_fast);
+        for (auto& v : empty_av) {
+            (void) v;
+            CHECK(false);
+        }
+    }
+
+    {
+        multi_span<int> empty_av = {};
+        CHECK(empty_av.bounds().index_bounds() == multi_span_index<1>{0});
+        CHECK_THROWS_AS(empty_av[0], fail_fast);
+        CHECK_THROWS_AS(empty_av.begin()[0], fail_fast);
+        CHECK_THROWS_AS(empty_av.cbegin()[0], fail_fast);
+        for (auto& v : empty_av) {
+            (void) v;
+            CHECK(false);
+        }
+    }
+}
+
+TEST_CASE("index_constructor")
+{
+    auto arr = new int[8];
+    for (int i = 0; i < 4; ++i) {
+        arr[2 * i] = 4 + i;
+        arr[2 * i + 1] = i;
+    }
+
+    multi_span<int, dynamic_range> av(arr, 8);
+
+    ptrdiff_t a[1] = {0};
+    multi_span_index<1> i = a;
+
+    CHECK(av[i] == 4);
+
+    auto av2 = as_multi_span(av, dim<4>(), dim(2));
+    ptrdiff_t a2[2] = {0, 1};
+    multi_span_index<2> i2 = a2;
+
+    CHECK(av2[i2] == 0);
+    CHECK(av2[0][i] == 4);
+
+    delete[] arr;
+}
+
+TEST_CASE("index_constructors")
+{
+    {
+        // components of the same type
+        multi_span_index<3> i1(0, 1, 2);
+        CHECK(i1[0] == 0);
+
+        // components of different types
+        std::size_t c0 = 0;
+        std::size_t c1 = 1;
+        multi_span_index<3> i2(c0, c1, 2);
+        CHECK(i2[0] == 0);
+
+        // from array
+        multi_span_index<3> i3 = {0, 1, 2};
+        CHECK(i3[0] == 0);
+
+        // from other index of the same size type
+        multi_span_index<3> i4 = i3;
+        CHECK(i4[0] == 0);
+
+        // default
+        multi_span_index<3> i7;
+        CHECK(i7[0] == 0);
+
+        // default
+        multi_span_index<3> i9 = {};
+        CHECK(i9[0] == 0);
+    }
+
+    {
+        // components of the same type
+        multi_span_index<1> i1(0);
+        CHECK(i1[0] == 0);
+
+        // components of different types
+        std::size_t c0 = 0;
+        multi_span_index<1> i2(c0);
+        CHECK(i2[0] == 0);
+
+        // from array
+        multi_span_index<1> i3 = {0};
+        CHECK(i3[0] == 0);
+
+        // from int
+        multi_span_index<1> i4 = 0;
+        CHECK(i4[0] == 0);
+
+        // from other index of the same size type
+        multi_span_index<1> i5 = i3;
+        CHECK(i5[0] == 0);
+
+        // default
+        multi_span_index<1> i8;
+        CHECK(i8[0] == 0);
+
+        // default
+        multi_span_index<1> i9 = {};
+        CHECK(i9[0] == 0);
+    }
+
+    #ifdef CONFIRM_COMPILATION_ERRORS
+    {
+    multi_span_index<3> i1(0, 1);
+    multi_span_index<3> i2(0, 1, 2, 3);
+    multi_span_index<3> i3 = {0};
+    multi_span_index<3> i4 = {0, 1, 2, 3};
+    multi_span_index<1> i5 = {0, 1};
+    }
+    #endif
+}
+
+TEST_CASE("index_operations")
+{
+    ptrdiff_t a[3] = {0, 1, 2};
+    ptrdiff_t b[3] = {3, 4, 5};
+    multi_span_index<3> i = a;
+    multi_span_index<3> j = b;
+
+    CHECK(i[0] == 0);
+    CHECK(i[1] == 1);
+    CHECK(i[2] == 2);
+
+    {
+        multi_span_index<3> k = i + j;
+
+        CHECK(i[0] == 0);
+        CHECK(i[1] == 1);
+        CHECK(i[2] == 2);
+        CHECK(k[0] == 3);
+        CHECK(k[1] == 5);
+        CHECK(k[2] == 7);
+    }
+
+    {
+        multi_span_index<3> k = i * 3;
+
+        CHECK(i[0] == 0);
+        CHECK(i[1] == 1);
+        CHECK(i[2] == 2);
+        CHECK(k[0] == 0);
+        CHECK(k[1] == 3);
+        CHECK(k[2] == 6);
+    }
+
+    {
+        multi_span_index<3> k = 3 * i;
+
+        CHECK(i[0] == 0);
+        CHECK(i[1] == 1);
+        CHECK(i[2] == 2);
+        CHECK(k[0] == 0);
+        CHECK(k[1] == 3);
+        CHECK(k[2] == 6);
+    }
+
+    {
+        multi_span_index<2> k = details::shift_left(i);
+
+        CHECK(i[0] == 0);
+        CHECK(i[1] == 1);
+        CHECK(i[2] == 2);
+        CHECK(k[0] == 1);
+        CHECK(k[1] == 2);
+    }
+}
+
+void iterate_second_column(multi_span<int, dynamic_range, dynamic_range> av)
+{
+    auto length = av.size() / 2;
+
+    // view to the second column
+    auto section = av.section({0, 1}, {length, 1});
+
+    CHECK(section.size() == length);
+    for (auto i = 0; i < section.size(); ++i) {
+        CHECK(section[i][0] == av[i][1]);
+    }
+
+    for (auto i = 0; i < section.size(); ++i) {
+        auto idx = multi_span_index<2>{i, 0}; // avoid braces inside the CHECK macro
+        CHECK(section[idx] == av[i][1]);
+    }
+
+    CHECK(section.bounds().index_bounds()[0] == length);
+    CHECK(section.bounds().index_bounds()[1] == 1);
+    for (auto i = 0; i < section.bounds().index_bounds()[0]; ++i) {
+        for (auto j = 0; j < section.bounds().index_bounds()[1]; ++j) {
+            auto idx = multi_span_index<2>{i, j}; // avoid braces inside the CHECK macro
+            CHECK(section[idx] == av[i][1]);
+        }
+    }
+
+    auto check_sum = 0;
+    for (auto i = 0; i < length; ++i) {
+        check_sum += av[i][1];
+    }
+
+    {
+        auto idx = 0;
+        auto sum = 0;
+        for (auto num : section) {
+            CHECK(num == av[idx][1]);
+            sum += num;
+            idx++;
+        }
+
+        CHECK(sum == check_sum);
+    }
+    {
+        auto idx = length - 1;
+        auto sum = 0;
+        for (auto iter = section.rbegin(); iter != section.rend(); ++iter) {
+            CHECK(*iter == av[idx][1]);
+            sum += *iter;
+            idx--;
+        }
+
+        CHECK(sum == check_sum);
+    }
+}
+
+TEST_CASE("span_section_iteration")
+{
+    int arr[4][2] = {{4, 0}, {5, 1}, {6, 2}, {7, 3}};
+
+    // static bounds
+    {
+        multi_span<int, 4, 2> av = arr;
+        iterate_second_column(av);
+    }
+    // first bound is dynamic
+    {
+        multi_span<int, dynamic_range, 2> av = arr;
+        iterate_second_column(av);
+    }
+    // second bound is dynamic
+    {
+        multi_span<int, 4, dynamic_range> av = arr;
+        iterate_second_column(av);
+    }
+    // both bounds are dynamic
+    {
+        multi_span<int, dynamic_range, dynamic_range> av = arr;
+        iterate_second_column(av);
+    }
+}
+
+TEST_CASE("dynamic_span_section_iteration")
+{
+    auto height = 4, width = 2;
+    auto size = height * width;
+
+    auto arr = new int[static_cast<std::size_t>(size)];
+    for (auto i = 0; i < size; ++i) {
+        arr[i] = i;
+    }
+
+    auto av = as_multi_span(arr, size);
+
+    // first bound is dynamic
+    {
+        multi_span<int, dynamic_range, 2> av2 = as_multi_span(av, dim(height), dim(width));
+        iterate_second_column(av2);
+    }
+    // second bound is dynamic
+    {
+        multi_span<int, 4, dynamic_range> av2 = as_multi_span(av, dim(height), dim(width));
+        iterate_second_column(av2);
+    }
+    // both bounds are dynamic
+    {
+        multi_span<int, dynamic_range, dynamic_range> av2 =
+            as_multi_span(av, dim(height), dim(width));
+        iterate_second_column(av2);
+    }
+
+    delete[] arr;
+}
+
+TEST_CASE("span_structure_size")
+{
+    double(*arr)[3][4] = new double[100][3][4];
+    multi_span<double, dynamic_range, 3, 4> av1(arr, 10);
+
+    struct EffectiveStructure
+    {
+        double* v1;
+        ptrdiff_t v2;
+    };
+    CHECK(sizeof(av1) == sizeof(EffectiveStructure));
+
+    CHECK_THROWS_AS(av1[10][3][4], fail_fast);
+
+    multi_span<const double, dynamic_range, 6, 4> av2 =
+        as_multi_span(av1, dim(5), dim<6>(), dim<4>());
+    (void) av2;
+}
+
+TEST_CASE("fixed_size_conversions")
+{
+    int arr[] = {1, 2, 3, 4};
+
+    // converting to an multi_span from an equal size array is ok
+    multi_span<int, 4> av4 = arr;
+    CHECK(av4.length() == 4);
+
+    // converting to dynamic_range a_v is always ok
+    {
+        multi_span<int, dynamic_range> av = av4;
+        (void) av;
+    }
+    {
+        multi_span<int, dynamic_range> av = arr;
+        (void) av;
+    }
+
+// initialization or assignment to static multi_span that REDUCES size is NOT ok
+#ifdef CONFIRM_COMPILATION_ERRORS
+    {
+        multi_span<int, 2> av2 = arr;
+    }
+    {
+        multi_span<int, 2> av2 = av4;
+    }
+#endif
+
+    {
+        multi_span<int, dynamic_range> av = arr;
+        multi_span<int, 2> av2 = av;
+        (void) av2;
+    }
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+    {
+        multi_span<int, dynamic_range> av = arr;
+        multi_span<int, 2, 1> av2 = av.as_multi_span(dim<2>(), dim<2>());
+    }
+#endif
+
+    {
+        multi_span<int, dynamic_range> av = arr;
+        multi_span<int, 2, 1> av2 = as_multi_span(av, dim(2), dim(2));
+        auto workaround_macro = [&]() { return av2[{1, 0}] == 2; };
+        CHECK(workaround_macro());
+    }
+
+    // but doing so explicitly is ok
+
+    // you can convert statically
+    {
+        multi_span<int, 2> av2 = {arr, 2};
+        (void) av2;
+    }
+    {
+        multi_span<int, 1> av2 = av4.first<1>();
+        (void) av2;
+    }
+
+    // ...or dynamically
+    {
+        // NB: implicit conversion to multi_span<int,2> from multi_span<int,dynamic_range>
+        multi_span<int, 1> av2 = av4.first(1);
+        (void) av2;
+    }
+
+    // initialization or assignment to static multi_span that requires size INCREASE is not ok.
+    int arr2[2] = {1, 2};
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+    {
+        multi_span<int, 4> av4 = arr2;
+    }
+    {
+        multi_span<int, 2> av2 = arr2;
+        multi_span<int, 4> av4 = av2;
+    }
+#endif
+    {
+        auto f = [&]() {
+            multi_span<int, 4> av9 = {arr2, 2};
+            (void) av9;
+        };
+        CHECK_THROWS_AS(f(), fail_fast);
+    }
+
+    // this should fail - we are trying to assign a small dynamic a_v to a fixed_size larger one
+    multi_span<int, dynamic_range> av = arr2;
+    auto f = [&]() {
+        multi_span<int, 4> av2 = av;
+        (void) av2;
+    };
+    CHECK_THROWS_AS(f(), fail_fast);
+}
+
+TEST_CASE("as_writeable_bytes")
+{
+    int a[] = {1, 2, 3, 4};
+
+    {
+#ifdef CONFIRM_COMPILATION_ERRORS
+        // you should not be able to get writeable bytes for const objects
+        multi_span<const int, dynamic_range> av = a;
+        auto wav = av.as_writeable_bytes();
+#endif
+    }
+
+    {
+        multi_span<int, dynamic_range> av;
+        auto wav = as_writeable_bytes(av);
+        CHECK(wav.length() == av.length());
+        CHECK(wav.length() == 0);
+        CHECK(wav.size_bytes() == 0);
+    }
+
+    {
+        multi_span<int, dynamic_range> av = a;
+        auto wav = as_writeable_bytes(av);
+        CHECK(wav.data() == reinterpret_cast<byte*>(&a[0]));
+        CHECK(static_cast<std::size_t>(wav.length()) == sizeof(a));
+    }
+}
+
+TEST_CASE("iterator")
+{
+    int a[] = {1, 2, 3, 4};
+
+    {
+        multi_span<int, dynamic_range> av = a;
+        auto wav = as_writeable_bytes(av);
+        for (auto& b : wav) {
+            b = byte(0);
+        }
+        for (std::size_t i = 0; i < 4; ++i) {
+            CHECK(a[i] == 0);
+        }
+    }
+
+    {
+        multi_span<int, dynamic_range> av = a;
+        for (auto& n : av) {
+            n = 1;
+        }
+        for (std::size_t i = 0; i < 4; ++i) {
+            CHECK(a[i] == 1);
+        }
+    }
+}