diff --git a/test/units/hic/file_writer_test.cpp b/test/units/hic/file_writer_test.cpp
index 4cba153cc..166bbcb4d 100644
--- a/test/units/hic/file_writer_test.cpp
+++ b/test/units/hic/file_writer_test.cpp
@@ -88,40 +88,57 @@ TEST_CASE("HiC: HiCInteractionToBlockMapper", "[hic][v9][short]") {
   CHECK(num_interactions == pixels1.size() + pixels2.size());
 }
 
-TEST_CASE("HiC: HiCFileWriter", "[hic][v9][short]") {
-  const auto path1 = (datadir / "4DNFIZ1ZVXC8.hic9").string();
-  const auto path2 = (testdir() / "hic_writer_001.hic").string();
-  const auto path3 = (testdir() / "hic_writer_002.hic").string();
-  const std::vector<std::uint32_t> resolutions{500'000, 1'000'000, 2'500'000};
-
-  SECTION("create file") {
-    {
-      const auto chromosomes = hic::File(path1, resolutions.front()).chromosomes();
-      HiCFileWriter w(path2, chromosomes, resolutions, "dm6", 3);
-      for (std::size_t i = 0; i < resolutions.size(); ++i) {
-        if (i % 2 == 0) {
-          const auto resolution = resolutions[i];
-          const hic::File f((datadir / "4DNFIZ1ZVXC8.hic9").string(), resolution);
-          const auto sel = f.fetch();
-          w.add_pixels(resolution, sel.begin<float>(), sel.end<float>());
-        }
+// NOLINTNEXTLINE(readability-function-cognitive-complexity)
+static void hic_file_writer_create_file_test(const std::string& path1, const std::string& path2,
+                                             const std::vector<std::uint32_t>& resolutions,
+                                             std::size_t num_threads) {
+  {
+    const auto chromosomes = hic::File(path1, resolutions.front()).chromosomes();
+    std::filesystem::remove(path2);
+    HiCFileWriter w(path2, chromosomes, resolutions, "dm6", num_threads);
+    for (std::size_t i = 0; i < resolutions.size(); ++i) {
+      if (i % 2 == 0) {
+        const auto resolution = resolutions[i];
+        const hic::File f((datadir / "4DNFIZ1ZVXC8.hic9").string(), resolution);
+        const auto sel1 = f.fetch("chr3R");
+        const auto sel2 = f.fetch("chr3R", "chr4");
+        w.add_pixels(resolution, sel1.begin<float>(), sel1.end<float>());
+        w.add_pixels(resolution, sel2.begin<float>(), sel2.end<float>());
       }
-      w.serialize();
     }
+    w.serialize();
+  }
 
-    for (const auto& resolution : resolutions) {
-      fmt::print(FMT_STRING("Comparing {}...\n"), resolution);
-      const hic::File f1(path1, resolution);
-      const hic::File f2(path2, resolution);
-      const auto expected_pixels = f1.fetch().read_all<float>();
-      const auto pixels = f2.fetch().read_all<float>();
+  for (const auto& resolution : resolutions) {
+    fmt::print(FMT_STRING("Comparing {}...\n"), resolution);
+    const hic::File f1(path1, resolution);
+    const hic::File f2(path2, resolution);
 
-      REQUIRE(expected_pixels.size() == pixels.size());
-      for (std::size_t i = 0; i < pixels.size(); ++i) {
-        CHECK(expected_pixels[i] == pixels[i]);
-      }
+    const auto expected_pixels1 = f1.fetch("chr3R").read_all<float>();
+    const auto expected_pixels2 = f1.fetch("chr3R", "chr4").read_all<float>();
+    const auto pixels1 = f2.fetch("chr3R").read_all<float>();
+    const auto pixels2 = f2.fetch("chr3R", "chr4").read_all<float>();
+
+    REQUIRE(expected_pixels1.size() == pixels1.size());
+    for (std::size_t i = 0; i < pixels1.size(); ++i) {
+      CHECK(expected_pixels1[i] == pixels1[i]);
+    }
+    REQUIRE(expected_pixels2.size() == pixels2.size());
+    for (std::size_t i = 0; i < pixels2.size(); ++i) {
+      CHECK(expected_pixels2[i] == pixels2[i]);
     }
   }
+}
+
+// NOLINTNEXTLINE(readability-function-cognitive-complexity)
+TEST_CASE("HiC: HiCFileWriter", "[hic][v9][short]") {
+  const auto path1 = (datadir / "4DNFIZ1ZVXC8.hic9").string();
+  const auto path2 = (testdir() / "hic_writer_001.hic").string();
+  const auto path3 = (testdir() / "hic_writer_002.hic").string();
+  const std::vector<std::uint32_t> resolutions{25'000, 250'000, 500'000};
+
+  SECTION("create file (st)") { hic_file_writer_create_file_test(path1, path2, resolutions, 1); }
+  SECTION("create file (mt)") { hic_file_writer_create_file_test(path1, path2, resolutions, 3); }
 
   SECTION("add weights") {
     const std::uint32_t resolution = 500'000;