Add FakeNif

config/config.exs

@@ -7,4 +7,5 @@ if Mix.env in [:test, :test_phoenix, :test_no_nif] do
     handle_sasl_reports: false
 
   config :appsignal, appsignal_system: Appsignal.FakeSystem
+  config :appsignal, appsignal_nif: Appsignal.FakeNif
 end

lib/appsignal/nif.ex

@@ -1,4 +1,9 @@
+defmodule Appsignal.NifBehaviour do
+  @callback loaded?() :: boolean()
+end
+
 defmodule Appsignal.Nif do
+  @behaviour Appsignal.NifBehaviour
   @moduledoc """
 
   It's a NIF! Oh no!

lib/mix/tasks/appsignal.diagnose.ex

@@ -3,6 +3,7 @@ defmodule Mix.Tasks.Appsignal.Diagnose do
   use Mix.Task
 
   @system Application.get_env(:appsignal, :appsignal_system, Appsignal.System)
+  @nif Application.get_env(:appsignal, :appsignal_nif, Appsignal.Nif)
 
   @shortdoc "Starts and tests AppSignal while validating the configuration."
 
@@ -44,7 +45,7 @@ defmodule Mix.Tasks.Appsignal.Diagnose do
 
     agent_info = Poison.decode!(File.read!(Path.expand("../../../agent.json", __DIR__)))
     IO.puts "  Agent version: #{agent_info["version"]}"
-    IO.puts "  Nif loaded: #{yes_or_no(Appsignal.Nif.loaded?)}"
+    IO.puts "  Nif loaded: #{yes_or_no(@nif.loaded?)}"
   end
 
   defp host_information do

test/mix/tasks/appsignal_diagnose_test.exs

@@ -4,13 +4,16 @@ defmodule Mix.Tasks.Appsignal.DiagnoseTest do
   import Mock
 
   @system Application.get_env(:appsignal, :appsignal_system, Appsignal.System)
+  @nif Application.get_env(:appsignal, :appsignal_nif, Appsignal.Nif)
 
   defp run do
     capture_io(fn -> Mix.Tasks.Appsignal.Diagnose.run(nil) end)
   end
 
   setup do
     @system.start_link
+    @nif.start_link
+
     original_config = appsignal_config()
 
     # By default, Push API key is valid
@@ -56,7 +59,9 @@ defmodule Mix.Tasks.Appsignal.DiagnoseTest do
   end
 
   describe "when Nif is not loaded" do
-    test_with_mock "outputs that the Nif is not loaded", Appsignal.Nif, [:passthrough], [loaded?: fn -> false end] do
+    setup do: @nif.set(:loaded?, false)
+
+    test "outputs that the Nif is not loaded" do
       output = run()
       assert String.contains? output, "Nif loaded: no"
     end

test/support/fake_nif.ex

@@ -0,0 +1,19 @@
+defmodule Appsignal.FakeNif do
+  @behaviour Appsignal.NifBehaviour
+
+  def start_link do
+    Agent.start_link(fn -> %{} end, name: __MODULE__)
+  end
+
+  def set(key, value) do
+    Agent.update(__MODULE__, &Map.put(&1, key, value))
+  end
+
+  def loaded? do
+    Agent.get(__MODULE__, &Map.get(&1, :loaded?, true))
+  end
+
+  def running_in_container? do
+    Agent.get(__MODULE__, &Map.get(&1, :running_in_container?, true))
+  end
+end