diff --git a/test/fd/atomic.cpp b/test/fd/atomic.cpp
new file mode 100644
index 0000000..c67ce41
--- /dev/null
+++ b/test/fd/atomic.cpp
@@ -0,0 +1,71 @@
+#include <filesystem>
+#include <memory>
+#include <stdplus/fd/atomic.hpp>
+#include <stdplus/fd/ops.hpp>
+#include <stdplus/gtest/tmp.hpp>
+#include <string_view>
+
+namespace stdplus
+{
+namespace fd
+{
+
+using std::literals::string_view_literals::operator""sv;
+
+class AtomicWriterTest : public gtest::TestWithTmp
+{
+  protected:
+    std::string filename;
+    std::unique_ptr<AtomicWriter> file;
+
+    AtomicWriterTest() : filename(fmt::format("{}/out", CaseTmpDir()))
+    {
+    }
+
+    ~AtomicWriterTest() noexcept
+    {
+        if (file)
+        {
+            auto tmpname = file->getTmpname();
+            file.reset();
+            if (!tmpname.empty())
+            {
+                EXPECT_FALSE(std::filesystem::exists(tmpname));
+            }
+        }
+    }
+};
+
+TEST_F(AtomicWriterTest, NoCommit)
+{
+    ASSERT_NO_THROW(file = std::make_unique<AtomicWriter>(filename, 0644));
+    writeExact(*file, "hi\n"sv);
+    EXPECT_FALSE(std::filesystem::exists(filename));
+    EXPECT_TRUE(std::filesystem::exists(file->getTmpname()));
+}
+
+TEST_F(AtomicWriterTest, BadCommit)
+{
+    auto tmp = fmt::format("{}/tmp.XXXXXX", CaseTmpDir());
+    ASSERT_NO_THROW(file =
+                        std::make_unique<AtomicWriter>("/dev/null", 0644, tmp));
+    writeExact(*file, "hi\n"sv);
+    EXPECT_TRUE(std::filesystem::exists(file->getTmpname()));
+    EXPECT_THROW(file->commit(), std::filesystem::filesystem_error);
+    EXPECT_EQ(file->getTmpname(), ""sv);
+}
+
+TEST_F(AtomicWriterTest, Basic)
+{
+    ASSERT_NO_THROW(file = std::make_unique<AtomicWriter>(filename, 0644));
+    writeExact(*file, "hi\n"sv);
+    EXPECT_TRUE(std::filesystem::exists(file->getTmpname()));
+    EXPECT_NO_THROW(file->commit());
+    EXPECT_EQ(file->getTmpname(), ""sv);
+    std::error_code ec;
+    EXPECT_EQ(3, std::filesystem::file_size(filename, ec));
+    EXPECT_EQ(std::errc{}, ec);
+}
+
+} // namespace fd
+} // namespace stdplus
diff --git a/test/fd/fmt.cpp b/test/fd/fmt.cpp
index 55f6c5d..f7ff9d8 100644
--- a/test/fd/fmt.cpp
+++ b/test/fd/fmt.cpp
@@ -1,11 +1,8 @@
 #include <gtest/gtest.h>
 
-#include <filesystem>
 #include <fmt/compile.h>
-#include <memory>
 #include <stdplus/fd/fmt.hpp>
 #include <stdplus/fd/managed.hpp>
-#include <stdplus/gtest/tmp.hpp>
 #include <stdplus/util/cexec.hpp>
 #include <sys/mman.h>
 
@@ -42,45 +39,5 @@
     EXPECT_EQ(4109, fd.lseek(0, Whence::Cur));
 }
 
-class FormatToFileTest : public gtest::TestWithTmp
-{
-  protected:
-    std::string tmpname;
-    std::unique_ptr<FormatToFile> file;
-
-    FormatToFileTest() :
-        tmpname(fmt::format("{}/tmp.XXXXXX", CaseTmpDir())),
-        file(std::make_unique<FormatToFile>(tmpname))
-    {
-        tmpname = file->getTmpname();
-        EXPECT_TRUE(std::filesystem::exists(tmpname));
-    }
-
-    ~FormatToFileTest() noexcept(true)
-    {
-        file.reset();
-        EXPECT_FALSE(std::filesystem::exists(tmpname));
-    }
-};
-
-TEST_F(FormatToFileTest, NoCommit)
-{
-    file->append("hi\n");
-    EXPECT_EQ(0, std::filesystem::file_size(tmpname));
-}
-
-TEST_F(FormatToFileTest, Basic)
-{
-    file->append("hi\n");
-    file->append("hi\n"sv);
-    file->append(FMT_STRING("hi\n"));
-    file->append(FMT_COMPILE("hi\n"));
-    EXPECT_EQ(0, std::filesystem::file_size(tmpname));
-    auto filename = fmt::format("{}/out", CaseTmpDir());
-    file->commit(filename);
-    EXPECT_FALSE(std::filesystem::exists(tmpname));
-    EXPECT_EQ(12, std::filesystem::file_size(filename));
-}
-
 } // namespace fd
 } // namespace stdplus
diff --git a/test/meson.build b/test/meson.build
index 7aada4a..452edae 100644
--- a/test/meson.build
+++ b/test/meson.build
@@ -23,6 +23,7 @@
   gtests += {
     'fd/dupable': [stdplus_fd_dep],
     'fd/managed': [stdplus_fd_dep],
+    'fd/fmt': [stdplus_fd_dep, stdplus_dep, gtest_main_dep],
     'fd/intf': [stdplus_fd_dep],
     'fd/impl': [stdplus_fd_dep],
     'fd/line': [stdplus_fd_dep, stdplus_dep, gmock_dep, gtest_main_dep],
@@ -32,12 +33,12 @@
   }
   if has_gtest
     gtests += {
-      'fd/fmt': [stdplus_fd_dep, stdplus_gtest_dep, stdplus_dep, gtest_main_dep],
+      'fd/atomic': [stdplus_fd_dep, stdplus_gtest_dep, gtest_main_dep],
     }
   elif build_tests.enabled()
-    error('Not testing fd/fmt feature')
+    error('Not testing fd/atomic feature')
   else
-    warning('Not testing fd/fmt feature')
+    warning('Not testing fd/atomic feature')
   endif
 elif build_tests.enabled()
   error('Not testing file descriptor feature')