diff --git a/include/fmt/async.h b/include/fmt/async.h
index 9938d7c7..4f81df61 100644
--- a/include/fmt/async.h
+++ b/include/fmt/async.h
@@ -90,6 +90,7 @@ namespace async {
 namespace detail {
 namespace detail = fmt::detail;
 template <typename T> using decay_t = typename std::decay<T>::type;
+template <typename T> using add_const_t = typename std::add_const<T>::type;
 
 enum class store_method {
     numeric,        // stored by libfmt as numeric value, no need for extra storage
@@ -188,7 +189,7 @@ struct arg_transformer {
 
 template <typename Arg, typename Context, typename Type = detail::mapped_type_constant<remove_reference_t<Arg>, Context>>
 using transformed_arg_type = conditional_t<custom_store_method<Arg, Context>::custom_store, typename custom_store_method<Arg, Context>::transformed_type,
-                             conditional_t<stored_as_string<Type>::value && !stored_as_string_object<Type, Arg>::value, basic_string_view<typename Context::char_type>, std::add_const_t<remove_reference_t<Arg>>&>
+                             conditional_t<stored_as_string<Type>::value && !stored_as_string_object<Type, Arg>::value, basic_string_view<typename Context::char_type>, add_const_t<remove_reference_t<Arg>>&>
                              >;
 
 template <typename Context, typename... Args>
@@ -205,7 +206,7 @@ struct async_entry_constructor {
 private:
     using range = typename range_builder<0, sizeof...(Args)>::type;
     template <typename S, size_t... Indice>
-    constexpr async_entry_constructor(void* buf, const S& format_str, index_list<Indice...>, Args... args) : pEntry(reinterpret_cast<char*>(buf)), pBuffer(get_buffer_store(buf)) {
+    FMT_CONSTEXPR async_entry_constructor(void* buf, const S& format_str, index_list<Indice...>, Args... args) : pEntry(reinterpret_cast<char*>(buf)), pBuffer(get_buffer_store(buf)) {
         auto p = new(buf) Entry(format_str, store<Indice>(std::forward<Args>(args))...);
         p->set_dtor(Dtor::value ? Dtor::destruct : nullptr);
     }
@@ -257,7 +258,7 @@ private:
         return basic_string_view<typename Context::char_type>(pStart, sv.size());
     }
 
-    static constexpr char* get_buffer_store(void* buf) {
+    static FMT_CONSTEXPR char* get_buffer_store(void* buf) {
         char* const pentry = reinterpret_cast<char*>(buf);      // entry will be constructed here
         char* const pobjs = pentry + sizeof(Entry);             // objects will be stored starting here
         char* const pbufs = pobjs + get_obj_size();             // buffers will be stored starting here
diff --git a/include/fmt/test.cpp b/include/fmt/test.cpp
deleted file mode 100644
index ddfbc87a..00000000
--- a/include/fmt/test.cpp
+++ /dev/null
@@ -1,23 +0,0 @@
-#define FMT_HEADER_ONLY
-#include "async.h"
-
-using namespace fmt;
-
-#include <iostream>
-
-
-
-int main() {
-    fmt::print("entry header: {}\n", sizeof(basic_async_entry<format_context>));
-    auto entry = make_async_entry("The answer is {}\n", 42);
-    async::print(entry);
-
-    char buf[2000];
-    size_t size = store_async_entry(buf, "This {} is {}{}\n", "answer", std::to_string(4), 2);
-    fmt::print("entry size: {}\n", size);
-    auto& entryref1 = entry;
-    auto& entryref = reinterpret_cast<decltype(entryref1)>(buf[0]);
-    async::print(entryref);
-
-    std::cout << &entryref << "\n" << &(entryref.arg_store_) << "\n" << sizeof(entryref.arg_store_) << std::endl;
-}
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index 7ae5659d..2c1aa605 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -88,6 +88,7 @@ function(add_fmt_test name)
 endfunction()
 
 add_fmt_test(assert-test)
+add_fmt_test(async-test)
 add_fmt_test(chrono-test)
 add_fmt_test(color-test)
 add_fmt_test(core-test)
diff --git a/test/async-test.cc b/test/async-test.cc
new file mode 100644
index 00000000..0ab6a8bf
--- /dev/null
+++ b/test/async-test.cc
@@ -0,0 +1,103 @@
+
+#ifdef WIN32
+#  define _CRT_SECURE_NO_WARNINGS
+#endif
+
+#include "fmt/async.h"
+#include "gtest-extra.h"
+
+#define TWENTY_ARGS "{} {} {} {} {} {} {} {} {} {} {} {} {} {} {} {} {} {} {} {} "
+static const char multiple_brackets[] = TWENTY_ARGS;
+static fmt::string_view get_format_string(size_t num_args) { return fmt::string_view(&multiple_brackets[(20 - num_args)*3], num_args * 3); }
+
+namespace trivial_entry_test {
+template <typename... Args>
+inline void make_async_entry_test(Args&&... args) {
+    std::string formatted = fmt::format(std::forward<Args>(args)...);
+    // format_arg_store containing named_args are not copy-constructible, auto&& is required.
+    auto&& entry = fmt::make_async_entry(std::forward<Args>(args)...);
+    EXPECT_EQ(formatted, fmt::async::format(entry));
+}
+
+template <typename... Args>
+inline void make_async_entry_test_args(Args&&... args) {
+    make_async_entry_test(get_format_string(sizeof...(args)), std::forward<Args>(args)...);
+}
+
+void make_async_entry_and_alter(const std::string& s) {
+    std::string str = s;
+    std::string formatted = fmt::format("{}", str);
+    auto entry = fmt::make_async_entry("{}", str);
+    str.front() =  formatted.front() = '#';
+    str.back() = formatted.back() = '#';
+    EXPECT_EQ(formatted, fmt::format("{}", str));
+    EXPECT_EQ(formatted, fmt::async::format(entry));
+}
+}
+
+namespace stored_entry_test {
+static char buf[1 * 1024 * 1024] = {}; // 1M should be enough for this test
+static fmt::basic_async_entry<fmt::format_context>& entry = reinterpret_cast<fmt::basic_async_entry<fmt::format_context>&>(buf);
+
+template <typename... Args>
+inline void make_async_entry_test(Args&&... args) {
+    std::string formatted = fmt::format(std::forward<Args>(args)...);
+    // FIXME: how to test entry_size?
+    size_t entry_size = fmt::store_async_entry(buf, std::forward<Args>(args)...);
+    EXPECT_EQ(formatted, fmt::async::format(entry));
+}
+
+template <typename... Args>
+inline void make_async_entry_test_args(Args&&... args) {
+    make_async_entry_test(get_format_string(sizeof...(args)), std::forward<Args>(args)...);
+}
+
+void make_async_entry_and_alter(const std::string& s) {
+    std::string str = s;
+    std::string formatted = fmt::format("{}", str);
+    size_t entry_size = fmt::store_async_entry(buf, "{}", str);
+    str.front() = str.back() = '#';
+    EXPECT_EQ(formatted, fmt::async::format(entry));
+    formatted.front() = formatted.back() = '#';
+    EXPECT_EQ(formatted, fmt::format("{}", str));
+}
+}
+
+TEST(AsyncTest, TrivialEntry) {
+    using namespace trivial_entry_test;
+    // basic test
+    make_async_entry_test("The answer is {}", 42);
+    // index
+    make_async_entry_test("The answer of {2}*{1} is {0}", 42, 6, 7);
+
+    // named args
+    using namespace fmt::literals;
+    make_async_entry_test("The answer of {}*{a} is {product}", 6, "product"_a=42, "a"_a=7);
+
+    // long arg list (>=16, as max_packed_args = 15)
+    make_async_entry_test_args(short(1), (unsigned short)2, 3, 4U, 5L, 6UL, 7LL, 8ULL, 9.0F, 10.0, 11, 12, 13, 14, 15, 16, 17, 18);
+    make_async_entry_test(TWENTY_ARGS "{narg}", 1,2,3,4,5,6,7,8,9,0,1,2,3,4,5,6,7,8,9,0,0/*ignore*/,"narg"_a="bingo");
+
+    // this API copies only reference.
+    make_async_entry_and_alter("[change me]");
+}
+
+
+TEST(AsyncTest, StoredEntry) {
+    using namespace stored_entry_test;
+    // basic test
+    make_async_entry_test("The answer is {}", 42);
+    // index
+    make_async_entry_test("The answer of {2}*{1} is {0}", 42, 6, 7);
+
+    // named args
+    using namespace fmt::literals;
+    // make_async_entry_test("The answer of {}*{a} is {product}", 6, "product"_a=42, "a"_a=7);
+
+    // long arg list (>=16, as max_packed_args = 15)
+    make_async_entry_test_args(short(1), (unsigned short)2, 3, 4U, 5L, 6UL, 7LL, 8ULL, 9.0F, 10.0, 11, 12, 13, 14, 15, 16, 17, 18);
+    // make_async_entry_test(TWENTY_ARGS "{narg}", 1,2,3,4,5,6,7,8,9,0,1,2,3,4,5,6,7,8,9,0,0/*ignore*/,"narg"_a="bingo");
+
+    // this API copies only reference.
+    make_async_entry_and_alter("[change me]");
+}