diff --git a/test/aprsme/is_test.exs b/test/aprsme/is_test.exs
index 8133538..9a74d47 100644
--- a/test/aprsme/is_test.exs
+++ b/test/aprsme/is_test.exs
@@ -201,6 +201,74 @@ defmodule Aprsme.IsTest do
     end
   end
 
+  describe "send_message/1 when GenServer is running" do
+    test "calls into the live process" do
+      # Spawn a tiny GenServer registered as Aprsme.Is so send_message/1 hits
+      # the `_pid -> GenServer.call(__MODULE__, ...)` branch.
+      original = Process.whereis(Aprsme.Is)
+      if original, do: :erlang.unregister(Aprsme.Is)
+
+      {:ok, fake_pid} =
+        GenServer.start(__MODULE__.FakeIs, :ok)
+
+      Process.register(fake_pid, Aprsme.Is)
+
+      try do
+        # The fake responds with :ok to {:send_message, _} calls.
+        assert Aprsme.Is.send_message("hello") == :ok
+      after
+        if Process.whereis(Aprsme.Is) == fake_pid, do: :erlang.unregister(Aprsme.Is)
+        if original && !Process.whereis(Aprsme.Is), do: Process.register(original, Aprsme.Is)
+        if Process.alive?(fake_pid), do: GenServer.stop(fake_pid)
+      end
+    end
+  end
+
+  defmodule FakeIs do
+    @moduledoc false
+    use GenServer
+
+    def init(state), do: {:ok, state}
+    def handle_call({:send_message, _msg}, _from, state), do: {:reply, :ok, state}
+  end
+
+  describe "init/1 disable_connection branch in non-test env" do
+    test "init with non-test env + disable_connection=true returns {:stop, :test_environment_disabled}" do
+      original_env = Application.get_env(:aprsme, :env)
+      original_disable = Application.get_env(:aprsme, :disable_aprs_connection)
+
+      try do
+        Application.put_env(:aprsme, :env, :prod)
+        Application.put_env(:aprsme, :disable_aprs_connection, true)
+
+        # Hits do_init(:prod, true) — line 60 Logger.warning + {:stop, _}.
+        assert {:stop, :test_environment_disabled} = Aprsme.Is.init([])
+      after
+        Application.put_env(:aprsme, :env, original_env)
+        Application.put_env(:aprsme, :disable_aprs_connection, original_disable)
+      end
+    end
+  end
+
+  describe "start_link/1 in test env" do
+    test "starts and immediately returns an error due to {:stop, _} from init" do
+      # The GenServer link will exit when init returns {:stop, _}, so we run
+      # it in a temporarily trap-exit task to avoid taking down the test pid.
+      Process.flag(:trap_exit, true)
+
+      try do
+        result = Aprsme.Is.start_link([])
+
+        assert match?({:error, :test_environment_disabled}, result) or
+                 match?({:error, _}, result)
+      catch
+        :exit, _ -> :ok
+      after
+        Process.flag(:trap_exit, false)
+      end
+    end
+  end
+
   describe "handle_info(:aprsme_no_message_timeout, ...)" do
     test "ignores timeout when socket is nil" do
       state = build_state(%{socket: nil})