diff --git a/test/str/conv.cpp b/test/str/conv.cpp
new file mode 100644
index 0000000..3a2f41c
--- /dev/null
+++ b/test/str/conv.cpp
@@ -0,0 +1,163 @@
+#include <fmt/format.h>
+
+#include <stdplus/str/conv.hpp>
+
+#include <algorithm>
+#include <string_view>
+
+#include <gtest/gtest.h>
+
+namespace stdplus
+{
+
+struct TestValS
+{
+    static inline constexpr std::string_view value = "test";
+    static inline constexpr std::wstring_view wvalue = L"test";
+};
+
+template <>
+struct ToStr<TestValS>
+{
+    using type = TestValS;
+    static inline constexpr std::size_t buf_size = TestValS::value.size();
+
+    template <typename CharT>
+    constexpr std::basic_string_view<CharT> operator()(TestValS) const noexcept
+    {
+        if constexpr (std::is_same_v<char, CharT>)
+        {
+            return TestValS::value;
+        }
+        else
+        {
+            static_assert(std::is_same_v<wchar_t, CharT>);
+            return TestValS::wvalue;
+        }
+    }
+};
+
+static_assert(!detail::ToStrFixed<ToStr<TestValS>>);
+static_assert(detail::ToStrStatic<ToStr<TestValS>>);
+
+struct TestValF : TestValS
+{};
+
+template <>
+struct ToStr<TestValF>
+{
+    using type = TestValF;
+    static inline constexpr std::size_t buf_size = TestValF::value.size();
+
+    template <typename CharT>
+    constexpr CharT* operator()(CharT* buf, TestValF) const noexcept
+    {
+        return std::copy(TestValF::value.begin(), TestValF::value.end(), buf);
+    }
+};
+
+static_assert(detail::ToStrFixed<ToStr<TestValF>>);
+static_assert(!detail::ToStrStatic<ToStr<TestValF>>);
+
+struct TestValD : TestValS
+{};
+
+template <>
+struct ToStr<TestValD>
+{
+    using type = TestValD;
+
+    template <typename CharT>
+    constexpr void operator()(stdplus::BasicStrBuf<CharT>& buf, TestValD) const
+    {
+        auto ptr = buf.append(TestValD::value.size());
+        std::copy(TestValD::value.begin(), TestValD::value.end(), ptr);
+    }
+};
+
+static_assert(!detail::ToStrFixed<ToStr<TestValD>>);
+static_assert(!detail::ToStrStatic<ToStr<TestValD>>);
+
+} // namespace stdplus
+
+template <typename CharT>
+struct fmt::formatter<stdplus::TestValS, CharT> :
+    stdplus::Format<stdplus::ToStr<stdplus::TestValS>, CharT>
+{};
+
+template <typename CharT>
+struct fmt::formatter<stdplus::TestValF, CharT> :
+    stdplus::Format<stdplus::ToStr<stdplus::TestValF>, CharT>
+{};
+
+template <typename CharT>
+struct fmt::formatter<stdplus::TestValD, CharT> :
+    stdplus::Format<stdplus::ToStr<stdplus::TestValD>, CharT>
+{};
+
+namespace stdplus
+{
+
+TEST(ToStrAdapter, Static)
+{
+    StrBuf buf;
+    ToStrAdap<ToStr<TestValS>>{}(buf, TestValS{});
+    EXPECT_EQ("test", buf);
+    buf.reset();
+    auto ptr = buf.append(4);
+    EXPECT_EQ(4, ToStrAdap<ToStr<TestValS>>{}(ptr, TestValS{}) - ptr);
+    EXPECT_EQ("test", std::string_view(ptr, 4));
+}
+
+TEST(ToStrAdapter, Fixed)
+{
+    StrBuf buf;
+    ToStrAdap<ToStr<TestValF>>{}(buf, TestValF{});
+    EXPECT_EQ("test", buf);
+}
+
+TEST(ToStrAdapter, Dynamic)
+{
+    StrBuf buf;
+    ToStrAdap<ToStr<TestValD>>{}(buf, TestValD{});
+    EXPECT_EQ("test", buf);
+}
+
+TEST(ToStrHandle, Basic)
+{
+    EXPECT_EQ("test", (ToStrHandle<ToStr<TestValS>>{}({})));
+    EXPECT_EQ(L"test", (ToStrHandle<ToStr<TestValS>, wchar_t>{}({})));
+    EXPECT_EQ("test", (ToStrHandle<ToStr<TestValF>>{}({})));
+    EXPECT_EQ(L"test", (ToStrHandle<ToStr<TestValF>, wchar_t>{}({})));
+    EXPECT_EQ("test", (ToStrHandle<ToStr<TestValD>>{}({})));
+    EXPECT_EQ(L"test", (ToStrHandle<ToStr<TestValD>, wchar_t>{}({})));
+}
+
+TEST(Format, Basic)
+{
+    EXPECT_EQ("t test", fmt::format("t {}", TestValS{}));
+    EXPECT_EQ("t test", fmt::format("t {}", TestValF{}));
+    EXPECT_EQ("t test", fmt::format("t {}", TestValD{}));
+}
+
+template <>
+struct FromStr<TestValS>
+{
+    template <typename CharT>
+    constexpr TestValS operator()(std::basic_string_view<CharT> sv) const
+    {
+        if (sv == TestValS::value)
+        {
+            return TestValS{};
+        }
+        throw std::runtime_error("Invalid TestValS");
+    }
+};
+
+TEST(FromStr, Basic)
+{
+    EXPECT_NO_THROW(fromStr<TestValS>("test"));
+    EXPECT_THROW(fromStr<TestValS>("hi"), std::runtime_error);
+}
+
+} // namespace stdplus