diff --git a/Dockerfile b/Dockerfile
index af1ee3d..2483e99 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -9,8 +9,14 @@ ENV LANG=C.UTF-8
 # install build dependencies
 RUN apt update && \
     apt upgrade -y && \
-    apt install -y --no-install-recommends git build-essential nodejs yarnpkg && \
-    apt clean -y && rm -rf /var/lib/apt/lists/*
+    apt install -y --no-install-recommends git build-essential curl ca-certificates gnupg && \
+    mkdir -p /etc/apt/keyrings && \
+    curl -fsSL https://deb.nodesource.com/gpgkey/nodesource-repo.gpg.key | gpg --dearmor -o /etc/apt/keyrings/nodesource.gpg && \
+    echo "deb [signed-by=/etc/apt/keyrings/nodesource.gpg] https://deb.nodesource.com/node_22.x nodistro main" > /etc/apt/sources.list.d/nodesource.list && \
+    apt update && \
+    apt install -y --no-install-recommends nodejs && \
+    apt clean -y && rm -rf /var/lib/apt/lists/* && \
+    npm install -g yarn
 
 # prepare build dir
 RUN mkdir /app
@@ -31,7 +37,7 @@ RUN mix deps.compile
 
 # build assets
 COPY assets assets
-RUN cd assets && yarnpkg install && yarnpkg run webpack --mode production
+RUN cd assets && yarn install && yarn run webpack --mode production
 RUN mix phx.digest
 
 # build project
diff --git a/test/diff/tmp_dir_test.exs b/test/diff/tmp_dir_test.exs
index e95dddd..4943135 100644
--- a/test/diff/tmp_dir_test.exs
+++ b/test/diff/tmp_dir_test.exs
@@ -15,14 +15,16 @@ defmodule Diff.TmpDirTest do
   test "cleanup on normal process exit" do
     test_pid = self()
 
-    Task.start(fn ->
-      file = Diff.TmpDir.tmp_file("test")
-      dir = Diff.TmpDir.tmp_dir("test")
-      send(test_pid, {:paths, file, dir})
-    end)
-
+    {:ok, task_pid} =
+      Task.start(fn ->
+        file = Diff.TmpDir.tmp_file("test")
+        dir = Diff.TmpDir.tmp_dir("test")
+        send(test_pid, {:paths, file, dir})
+      end)
+
+    ref = Process.monitor(task_pid)
     assert_receive {:paths, file, dir}
-    Process.sleep(100)
+    wait_for_cleanup(task_pid, ref)
 
     refute File.exists?(file)
     refute File.exists?(dir)
@@ -32,15 +34,17 @@ defmodule Diff.TmpDirTest do
   test "cleanup on process crash" do
     test_pid = self()
 
-    Task.start(fn ->
-      file = Diff.TmpDir.tmp_file("test")
-      dir = Diff.TmpDir.tmp_dir("test")
-      send(test_pid, {:paths, file, dir})
-      raise "crash"
-    end)
+    {:ok, task_pid} =
+      Task.start(fn ->
+        file = Diff.TmpDir.tmp_file("test")
+        dir = Diff.TmpDir.tmp_dir("test")
+        send(test_pid, {:paths, file, dir})
+        raise "crash"
+      end)
 
+    ref = Process.monitor(task_pid)
     assert_receive {:paths, file, dir}
-    Process.sleep(100)
+    wait_for_cleanup(task_pid, ref)
 
     refute File.exists?(file)
     refute File.exists?(dir)
@@ -49,19 +53,21 @@ defmodule Diff.TmpDirTest do
   test "multiple paths for one process" do
     test_pid = self()
 
-    Task.start(fn ->
-      paths =
-        for i <- 1..5 do
-          file = Diff.TmpDir.tmp_file("test-#{i}")
-          dir = Diff.TmpDir.tmp_dir("test-#{i}")
-          {file, dir}
-        end
+    {:ok, task_pid} =
+      Task.start(fn ->
+        paths =
+          for i <- 1..5 do
+            file = Diff.TmpDir.tmp_file("test-#{i}")
+            dir = Diff.TmpDir.tmp_dir("test-#{i}")
+            {file, dir}
+          end
 
-      send(test_pid, {:paths, paths})
-    end)
+        send(test_pid, {:paths, paths})
+      end)
 
+    ref = Process.monitor(task_pid)
     assert_receive {:paths, paths}
-    Process.sleep(100)
+    wait_for_cleanup(task_pid, ref)
 
     for {file, dir} <- paths do
       refute File.exists?(file)
@@ -76,4 +82,10 @@ defmodule Diff.TmpDirTest do
     assert File.exists?(file)
     assert File.dir?(dir)
   end
+
+  defp wait_for_cleanup(task_pid, ref) do
+    assert_receive {:DOWN, ^ref, :process, ^task_pid, _}, 5000
+    # Sync with the GenServer to ensure the :DOWN cleanup has been processed
+    :sys.get_state(Diff.TmpDir)
+  end
 end