diff --git a/agent/test/proxmox_agent/diagnostics_test.exs b/agent/test/proxmox_agent/diagnostics_test.exs
index 867f358..000bfe2 100644
--- a/agent/test/proxmox_agent/diagnostics_test.exs
+++ b/agent/test/proxmox_agent/diagnostics_test.exs
@@ -61,4 +61,40 @@ defmodule ProxmoxAgent.DiagnosticsTest do
       assert :ok = Diagnostics.log_command("zpool", ["list"], {:ok, "body"}, 1_234)
     end
   end
+
+  describe "log_command/4 and log_sample/2 with writer running" do
+    setup do
+      dir = Path.join(System.tmp_dir!(), "diag-e2e-#{System.unique_integer([:positive])}")
+      File.mkdir_p!(dir)
+      :ok = Diagnostics.configure(dir)
+
+      {:ok, pid} = ProxmoxAgent.Diagnostics.Writer.start_link(dir: dir)
+
+      on_exit(fn ->
+        if Process.alive?(pid), do: GenServer.stop(pid)
+        File.rm_rf(dir)
+      end)
+
+      %{dir: dir}
+    end
+
+    test "log_command/4 writes to commands.log", %{dir: dir} do
+      assert :ok = Diagnostics.log_command("zpool", ["list", "-j"], {:ok, "body"}, 2_500)
+      :ok = GenServer.call(ProxmoxAgent.Diagnostics.Writer, :flush)
+
+      body = File.read!(Path.join(dir, "commands.log"))
+      assert body =~ "$ zpool list -j"
+      assert body =~ "exit=0"
+      assert body =~ "size=4"
+    end
+
+    test "log_sample/2 writes to samples.log", %{dir: dir} do
+      assert :ok = Diagnostics.log_sample("fast", %{"zfs_pools" => %{"pools" => []}})
+      :ok = GenServer.call(ProxmoxAgent.Diagnostics.Writer, :flush)
+
+      body = File.read!(Path.join(dir, "samples.log"))
+      assert body =~ "kind=fast"
+      assert body =~ "\"zfs_pools\""
+    end
+  end
 end