Reintroduce full server testing with different approach

Now we start manually all application children instead of ensuring the
application has started

Author: badosu

apps/expert/test/expert_test.exs

@@ -1,11 +1,83 @@
 defmodule Expert.ExpertTest do
-  use ExUnit.Case, async: true
+  alias Forge.Test.Fixtures
+
+  use ExUnit.Case, async: false
+  use Forge.Test.EventualAssertions
   use Patch
 
   require GenLSP.Test
 
   import Expert.Test.Protocol.TransportSupport
 
+  describe "server testing" do
+    defp buffer_opts do
+      [communication: {GenLSP.Communication.TCP, [port: 0]}]
+    end
+
+    defp start_application_children do
+      pids =
+        for child_spec <- Expert.Application.children(buffer: buffer_opts()) do
+          start_supervised!(child_spec)
+        end
+
+      on_exit(fn ->
+        # NOTE: The test hangs for some reason without manually exiting
+        for pid <- pids do
+          Process.exit(pid, :normal)
+        end
+      end)
+    end
+
+    setup do
+      start_application_children()
+
+      comm_state = GenLSP.Buffer.comm_state(Expert.Buffer)
+
+      {:ok, port} = :inet.port(comm_state.lsocket)
+      %{lsp: lsp} = :sys.get_state(Expert.Buffer)
+
+      expert = %{lsp: lsp, port: port}
+      client = GenLSP.Test.client(expert)
+
+      [expert: expert, client: client]
+    end
+
+    test "replies to initialize with expert info and capabilities", %{client: client} do
+      id = System.unique_integer([:positive])
+
+      project = Fixtures.project()
+
+      root_uri = project.root_uri
+      root_path = Forge.Project.root_path(project)
+
+      assert :ok ==
+               GenLSP.Test.request(client, %{
+                 "id" => id,
+                 "jsonrpc" => "2.0",
+                 "method" => "initialize",
+                 "params" => %{
+                   "rootPath" => root_path,
+                   "rootUri" => root_uri,
+                   "capabilities" => %{},
+                   "workspaceFolders" => [
+                     %{
+                       uri: root_uri,
+                       name: root_path
+                     }
+                   ]
+                 }
+               })
+
+      GenLSP.Test.assert_result(^id, result, 500)
+
+      {:ok, initialize_result} =
+        GenLSP.Requests.Initialize.result()
+        |> Schematic.dump(Expert.State.initialize_result())
+
+      assert result == initialize_result
+    end
+  end
+
   test "sends an error message on engine initialization error" do
     with_patched_transport()