diff --git a/tests/at_tests.cpp b/tests/at_tests.cpp
new file mode 100644
index 0000000..2f9e999
--- /dev/null
+++ b/tests/at_tests.cpp
@@ -0,0 +1,116 @@
+///////////////////////////////////////////////////////////////////////////////
+//
+// 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_THROW...
+
+#include <gsl/gsl_util> // for at
+
+#include <array>            // for array
+#include <cstddef>          // for size_t
+#include <initializer_list> // for initializer_list
+#include <vector>           // for vector
+
+namespace gsl {
+struct fail_fast;
+}  // namespace gsl
+
+using gsl::fail_fast;
+
+TEST_CASE("static_array")
+{
+    int a[4] = {1, 2, 3, 4};
+    const int(&c_a)[4] = a;
+
+    for (int i = 0; i < 4; ++i) {
+        CHECK(&gsl::at(a, i) == &a[i]);
+        CHECK(&gsl::at(c_a, i) == &a[i]);
+    }
+
+    CHECK_THROWS_AS(gsl::at(a, -1), fail_fast);
+    CHECK_THROWS_AS(gsl::at(a, 4), fail_fast);
+    CHECK_THROWS_AS(gsl::at(c_a, -1), fail_fast);
+    CHECK_THROWS_AS(gsl::at(c_a, 4), fail_fast);
+}
+
+TEST_CASE("std_array")
+{
+    std::array<int, 4> a = {1, 2, 3, 4};
+    const std::array<int, 4>& c_a = a;
+
+    for (int i = 0; i < 4; ++i) {
+        CHECK(&gsl::at(a, i) == &a[static_cast<std::size_t>(i)]);
+        CHECK(&gsl::at(c_a, i) == &a[static_cast<std::size_t>(i)]);
+    }
+
+    CHECK_THROWS_AS(gsl::at(a, -1), fail_fast);
+    CHECK_THROWS_AS(gsl::at(a, 4), fail_fast);
+    CHECK_THROWS_AS(gsl::at(c_a, -1), fail_fast);
+    CHECK_THROWS_AS(gsl::at(c_a, 4), fail_fast);
+}
+
+TEST_CASE("StdVector")
+{
+    std::vector<int> a = {1, 2, 3, 4};
+    const std::vector<int>& c_a = a;
+
+    for (int i = 0; i < 4; ++i) {
+        CHECK(&gsl::at(a, i) == &a[static_cast<std::size_t>(i)]);
+        CHECK(&gsl::at(c_a, i) == &a[static_cast<std::size_t>(i)]);
+    }
+
+    CHECK_THROWS_AS(gsl::at(a, -1), fail_fast);
+    CHECK_THROWS_AS(gsl::at(a, 4), fail_fast);
+    CHECK_THROWS_AS(gsl::at(c_a, -1), fail_fast);
+    CHECK_THROWS_AS(gsl::at(c_a, 4), fail_fast);
+}
+
+TEST_CASE("InitializerList")
+{
+    std::initializer_list<int> a = {1, 2, 3, 4};
+
+    for (int i = 0; i < 4; ++i) {
+        CHECK(gsl::at(a, i) == i + 1);
+        CHECK(gsl::at({1, 2, 3, 4}, i) == i + 1);
+    }
+
+    CHECK_THROWS_AS(gsl::at(a, -1), fail_fast);
+    CHECK_THROWS_AS(gsl::at(a, 4), fail_fast);
+    CHECK_THROWS_AS(gsl::at({1, 2, 3, 4}, -1), fail_fast);
+    CHECK_THROWS_AS(gsl::at({1, 2, 3, 4}, 4), fail_fast);
+}
+
+#if !defined(_MSC_VER) || defined(__clang__) || _MSC_VER >= 1910
+static constexpr bool test_constexpr()
+{
+    int a1[4] = {1, 2, 3, 4};
+    const int(&c_a1)[4] = a1;
+    std::array<int, 4> a2 = {1, 2, 3, 4};
+    const std::array<int, 4>& c_a2 = a2;
+
+    for (int i = 0; i < 4; ++i) {
+        if (&gsl::at(a1, i) != &a1[i]) return false;
+        if (&gsl::at(c_a1, i) != &a1[i]) return false;
+        // requires C++17:
+        // if (&gsl::at(a2, i) != &a2[static_cast<std::size_t>(i)]) return false;
+        if (&gsl::at(c_a2, i) != &c_a2[static_cast<std::size_t>(i)]) return false;
+        if (gsl::at({1, 2, 3, 4}, i) != i + 1) return false;
+    }
+
+    return true;
+}
+
+static_assert(test_constexpr(), "FAIL");
+#endif