diff --git a/.gitmodules b/.gitmodules
index 49f1431..007937d 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -1,3 +1,6 @@
 [submodule "external/xsimd"]
 	path = external/xsimd
 	url = https://github.com/xtensor-stack/xsimd.git
+[submodule "external/utest"]
+	path = external/utest
+	url = https://github.com/sheredom/utest.h.git
diff --git a/CMakeLists.txt b/CMakeLists.txt
index fff8c15..a0858a7 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -11,11 +11,12 @@ find_package(pybind11 CONFIG REQUIRED)
 find_package(OpenMP)
 
 add_subdirectory(external/xsimd)
+include_directories(external/utest)
 
 # Collect source files
 file(GLOB SOURCE_FILES
         "quicktex/*.cpp"
-        "quicktex/tests/*.cpp"
+        "quicktex/ctests/*.cpp"
         "quicktex/s3tc/*.cpp"
         "quicktex/s3tc/bc1/*.cpp"
         "quicktex/s3tc/bc3/*.cpp"
@@ -26,7 +27,7 @@ file(GLOB SOURCE_FILES
 
 file(GLOB HEADER_FILES
         "quicktex/*.h"
-        "quicktex/tests/*.h"
+        "quicktex/ctests/*.h"
         "quicktex/s3tc/*.h"
         "quicktex/s3tc/bc1/*.h"
         "quicktex/s3tc/bc3/*.h"
diff --git a/external/utest b/external/utest
new file mode 160000
index 0000000..06abbd1
--- /dev/null
+++ b/external/utest
@@ -0,0 +1 @@
+Subproject commit 06abbd1978f7e9c5f61642d80b9d300e3a8c4ccf
diff --git a/quicktex/_bindings.cpp b/quicktex/_bindings.cpp
index b71180b..c56f682 100644
--- a/quicktex/_bindings.cpp
+++ b/quicktex/_bindings.cpp
@@ -20,6 +20,7 @@
 #include "_bindings.h"
 
 #include <pybind11/pybind11.h>
+#include <utest.h>
 
 #include "Color.h"
 #include "Decoder.h"
@@ -30,12 +31,13 @@
 #define STRINGIFY(x) #x
 #define MACRO_STRINGIFY(x) STRINGIFY(x)
 
+UTEST_STATE();
+
 namespace py = pybind11;
 
 namespace quicktex::bindings {
 
 void InitS3TC(py::module_ &m);
-void InitCTests(py::module_ &m);
 
 PYBIND11_MODULE(_quicktex, m) {
     m.doc() = "More Stuff";
@@ -58,7 +60,8 @@ PYBIND11_MODULE(_quicktex, m) {
     texture.def_property_readonly("height", &Texture::Height);
 
     texture.def_buffer([](Texture &t) { return py::buffer_info(t.Data(), t.NBytes()); });
-    texture.def("tobytes", [](const Texture &t) { return py::bytes(reinterpret_cast<const char *>(t.Data()), t.NBytes()); });
+    texture.def("tobytes",
+                [](const Texture &t) { return py::bytes(reinterpret_cast<const char *>(t.Data()), t.NBytes()); });
 
     // RawTexture
 
@@ -70,7 +73,9 @@ PYBIND11_MODULE(_quicktex, m) {
     DefSubscript2D(raw_texture, &RawTexture::GetPixel, &RawTexture::SetPixel, &RawTexture::Size);
 
     InitS3TC(m);
-    InitCTests(m);
+
+    // CTests
+    m.def("_run_ctests", []() { return utest_main(0, NULL); });
 }
 
 }  // namespace quicktex::bindings
\ No newline at end of file
diff --git a/quicktex/ctests/TestSIMD.cpp b/quicktex/ctests/TestSIMD.cpp
new file mode 100644
index 0000000..9cd7f42
--- /dev/null
+++ b/quicktex/ctests/TestSIMD.cpp
@@ -0,0 +1,86 @@
+/*  Quicktex Texture Compression Library
+    Copyright (C) 2021 Andrew Cassidy <drewcassidy@me.com>
+    Partially derived from rgbcx.h written by Richard Geldreich <richgel99@gmail.com>
+    and licenced under the public domain
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU Lesser General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU Lesser General Public License for more details.
+
+    You should have received a copy of the GNU Lesser General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "TestSIMD.h"
+
+#include <utest.h>
+
+#include <array>
+#include <cassert>
+#include <cstdint>
+#include <numeric>
+#include <type_traits>
+#include <xsimd/xsimd.hpp>
+
+#include "../VecUtil.h"
+
+namespace quicktex::tests {
+
+template <typename T> constexpr auto make_arrays() {
+    std::vector<std::array<T, xsimd::batch<T>::size>> arrays;
+    std::array<T, xsimd::batch<T>::size> buffer;
+
+    std::iota(buffer.begin(), buffer.end(), 1);
+    arrays.push_back(buffer);
+
+    buffer.fill(1);
+    arrays.push_back(buffer);
+
+    buffer.fill(0);
+    arrays.push_back(buffer);
+
+    buffer.fill(std::numeric_limits<T>::max());
+    arrays.push_back(buffer);
+
+    if (std::is_signed_v<T>) {
+        std::iota(buffer.begin(), buffer.end(), -1);
+        arrays.push_back(buffer);
+
+        buffer.fill(-1);
+        arrays.push_back(buffer);
+
+        buffer.fill(std::numeric_limits<T>::min());
+        arrays.push_back(buffer);
+    }
+
+    return arrays;
+}
+
+template <typename T, size_t N> long int sumArray(std::array<T, N> const &arg) {
+    return std::accumulate(arg.begin(), arg.end(), (long)0);
+}
+
+#define UTEST_WHADD(TYPE)                            \
+    UTEST(simd, whadd_##TYPE) {                      \
+        for (auto arr : make_arrays<TYPE>()) {       \
+            auto v = xsimd::load_unaligned(&arr[0]); \
+            auto vsum = simd::whadd(v);              \
+            auto ssum = sumArray(arr);               \
+            ASSERT_EQ(vsum, ssum);                   \
+        }                                            \
+    }
+
+UTEST_WHADD(int8_t);
+UTEST_WHADD(uint8_t);
+UTEST_WHADD(int16_t);
+UTEST_WHADD(uint16_t);
+UTEST_WHADD(int32_t);
+UTEST_WHADD(uint32_t);
+
+}  // namespace quicktex::tests
\ No newline at end of file
diff --git a/quicktex/tests/TestSIMD.h b/quicktex/ctests/TestSIMD.h
similarity index 100%
rename from quicktex/tests/TestSIMD.h
rename to quicktex/ctests/TestSIMD.h
diff --git a/quicktex/tests/TestSIMD.cpp b/quicktex/tests/TestSIMD.cpp
deleted file mode 100644
index 7c1be9c..0000000
--- a/quicktex/tests/TestSIMD.cpp
+++ /dev/null
@@ -1,62 +0,0 @@
-/*  Quicktex Texture Compression Library
-    Copyright (C) 2021 Andrew Cassidy <drewcassidy@me.com>
-    Partially derived from rgbcx.h written by Richard Geldreich <richgel99@gmail.com>
-    and licenced under the public domain
-
-    This program is free software: you can redistribute it and/or modify
-    it under the terms of the GNU Lesser General Public License as published by
-    the Free Software Foundation, either version 3 of the License, or
-    (at your option) any later version.
-
-    This program is distributed in the hope that it will be useful,
-    but WITHOUT ANY WARRANTY; without even the implied warranty of
-    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-    GNU Lesser General Public License for more details.
-
-    You should have received a copy of the GNU Lesser General Public License
-    along with this program.  If not, see <http://www.gnu.org/licenses/>.
- */
-
-#include "TestSIMD.h"
-
-#include <array>
-#include <cassert>
-#include <cstdint>
-#include <numeric>
-
-#include <xsimd/xsimd.hpp>
-#include "../VecUtil.h"
-
-namespace quicktex::tests {
-
-void test_widening_hadd() {
-    const auto vec_size = xsimd::batch<int16_t>::size;
-    std::array<int16_t, vec_size> buffer;
-
-    std::iota(buffer.begin(), buffer.end(), 1);
-    auto v = xsimd::load_unaligned(&buffer[0]);
-    auto sum = simd::whadd(v);
-    assert(sum == vec_size / 2 * (vec_size + 1));  // Gauss formula
-
-    buffer.fill(1);
-    v = xsimd::load_unaligned(&buffer[0]);
-    sum = simd::whadd(v);
-    assert(sum == vec_size);
-
-    buffer.fill(0);
-    v = xsimd::load_unaligned(&buffer[0]);
-    sum = simd::whadd(v);
-    assert(sum == 0);
-
-    buffer.fill(std::numeric_limits<int16_t>::max());
-    v = xsimd::load_unaligned(&buffer[0]);
-    sum = simd::whadd(v);
-    assert(sum == std::numeric_limits<int16_t>::max() * (int)vec_size);
-
-    buffer.fill(std::numeric_limits<int16_t>::min());
-    v = xsimd::load_unaligned(&buffer[0]);
-    sum = simd::whadd(v);
-    assert(sum == std::numeric_limits<int16_t>::min() * (int)vec_size);
-
-}
-}  // namespace quicktex::tests
\ No newline at end of file
diff --git a/quicktex/tests/_bindings.cpp b/quicktex/tests/_bindings.cpp
deleted file mode 100644
index e5b18fc..0000000
--- a/quicktex/tests/_bindings.cpp
+++ /dev/null
@@ -1,44 +0,0 @@
-/*  Quicktex Texture Compression Library
-    Copyright (C) 2021 Andrew Cassidy <drewcassidy@me.com>
-    Partially derived from rgbcx.h written by Richard Geldreich <richgel99@gmail.com>
-    and licenced under the public domain
-
-    This program is free software: you can redistribute it and/or modify
-    it under the terms of the GNU Lesser General Public License as published by
-    the Free Software Foundation, either version 3 of the License, or
-    (at your option) any later version.
-
-    This program is distributed in the hope that it will be useful,
-    but WITHOUT ANY WARRANTY; without even the implied warranty of
-    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-    GNU Lesser General Public License for more details.
-
-    You should have received a copy of the GNU Lesser General Public License
-    along with this program.  If not, see <http://www.gnu.org/licenses/>.
- */
-
-#include "../_bindings.h"
-
-#include <pybind11/pybind11.h>
-#include <pybind11/stl.h>
-
-#include <array>
-#include <cstddef>
-#include <cstdint>
-#include <stdexcept>
-#include <string>
-
-#include "TestSIMD.h"
-
-namespace py = pybind11;
-namespace quicktex::bindings {
-
-using namespace pybind11::literals;
-using namespace quicktex::tests;
-
-void InitCTests(py::module_ &quicktex) {
-    py::module_ ctests = quicktex.def_submodule("_ctests", "Internal tests for C-level functions");
-
-//    ctests.def("test_WidenSumS16", &TestWidenSumS16);
-}
-}  // namespace quicktex::bindings
\ No newline at end of file
diff --git a/quicktex/util.h b/quicktex/util.h
index d0aff20..be7d936 100644
--- a/quicktex/util.h
+++ b/quicktex/util.h
@@ -181,6 +181,10 @@ template <class > struct next_size;
 template <class T> using next_size_t = typename next_size<T>::type;
 template <class T> struct Tag { using type = T; };
 
-template <> struct next_size<int_least8_t>  : Tag<int_least16_t> { };
-template <> struct next_size<int_least16_t> : Tag<int_least32_t> { };
-template <> struct next_size<int_least32_t> : Tag<int_least64_t> { };
\ No newline at end of file
+template <> struct next_size<int8_t>  : Tag<int16_t> { };
+template <> struct next_size<int16_t> : Tag<int32_t> { };
+template <> struct next_size<int32_t> : Tag<int64_t> { };
+
+template <> struct next_size<uint8_t>  : Tag<uint16_t> { };
+template <> struct next_size<uint16_t> : Tag<uint32_t> { };
+template <> struct next_size<uint32_t> : Tag<uint64_t> { };
\ No newline at end of file
diff --git a/tests/test_ctest.py b/tests/test_ctest.py
index 1c515e8..64e6b21 100644
--- a/tests/test_ctest.py
+++ b/tests/test_ctest.py
@@ -1,8 +1,5 @@
-import unittest
-
-import _quicktex._ctests as c
+from _quicktex import _run_ctests
 
 
-class TestCTest(unittest.TestCase):
-    def test_WidenSumS16(self):
-        c.test_WidenSumS16()
+def test_ctests():
+    _run_ctests()