diff --git a/test/default_session_registry_test.exs b/test/default_session_registry_test.exs
new file mode 100644
index 0000000..ead516c
--- /dev/null
+++ b/test/default_session_registry_test.exs
@@ -0,0 +1,42 @@
+defmodule ExFix.DefaultSessionRegistryTest do
+  use ExUnit.Case
+
+  alias ExFix.DefaultSessionRegistry
+
+  test "session_on_init replies according to status" do
+    table = :ex_fix_registry
+    :ets.delete_all_objects(table)
+
+    assert {:error, :notfound} = DefaultSessionRegistry.session_on_init("s1")
+
+    DefaultSessionRegistry.session_update_status("s2", :connecting)
+    assert :ok = DefaultSessionRegistry.session_on_init("s2")
+
+    DefaultSessionRegistry.session_update_status("s3", :connected)
+    assert :wait_to_reconnect = DefaultSessionRegistry.session_on_init("s3")
+
+    DefaultSessionRegistry.session_update_status("s4", :disconnecting)
+    assert {:error, :disconnected} = DefaultSessionRegistry.session_on_init("s4")
+  end
+
+  test "handles process DOWN messages" do
+    table = :ex_fix_registry
+    :ets.delete_all_objects(table)
+
+    DefaultSessionRegistry.session_update_status("dn1", :connecting)
+    :ok = DefaultSessionRegistry.session_on_init("dn1")
+    state = :sys.get_state(DefaultSessionRegistry)
+    ref1 = Enum.find_value(state.monitor_map, fn {ref, name} -> if name == "dn1", do: ref end)
+    send(DefaultSessionRegistry, {:DOWN, ref1, :process, self(), :normal})
+    Process.sleep(10)
+    assert DefaultSessionRegistry.get_session_status("dn1") == :disconnected
+
+    DefaultSessionRegistry.session_update_status("dn2", :connecting)
+    :ok = DefaultSessionRegistry.session_on_init("dn2")
+    state = :sys.get_state(DefaultSessionRegistry)
+    ref2 = Enum.find_value(state.monitor_map, fn {ref, name} -> if name == "dn2", do: ref end)
+    send(DefaultSessionRegistry, {:DOWN, ref2, :process, self(), :shutdown})
+    Process.sleep(10)
+    assert DefaultSessionRegistry.get_session_status("dn2") == :reconnecting
+  end
+end
diff --git a/test/ex_fix_api_test.exs b/test/ex_fix_api_test.exs
new file mode 100644
index 0000000..4e44d70
--- /dev/null
+++ b/test/ex_fix_api_test.exs
@@ -0,0 +1,57 @@
+defmodule ExFix.ApiTest do
+  use ExUnit.Case
+
+  alias ExFix.SessionConfig
+  alias ExFix.TestHelper.FixEmptySessionHandler
+
+  defmodule CaptureRegistry do
+    @behaviour ExFix.SessionRegistry
+
+    def get_session_status(_), do: :disconnected
+
+    def start_session(name, %SessionConfig{} = config) do
+      send(self(), {:start_session, name, config})
+      :ok
+    end
+
+    def stop_session(name) do
+      send(self(), {:stop_session, name})
+      :ok
+    end
+
+    def session_on_init(_), do: :ok
+    def session_update_status(_, _), do: :ok
+  end
+
+  test "start_session_initiator builds config and delegates" do
+    ExFix.start_session_initiator(
+      "test_sess",
+      "S",
+      "T",
+      FixEmptySessionHandler,
+      session_registry: CaptureRegistry,
+      hostname: "myhost",
+      port: 12_345,
+      log_incoming_msg: false
+    )
+
+    assert_receive {:start_session, "test_sess", config}
+    assert %SessionConfig{name: "test_sess", sender_comp_id: "S", target_comp_id: "T"} = config
+    assert config.hostname == "myhost"
+    assert config.port == 12_345
+    assert config.log_incoming_msg == false
+
+    ExFix.stop_session("test_sess", CaptureRegistry)
+    assert_receive {:stop_session, "test_sess"}
+  end
+
+  test "start_session_initiator uses defaults" do
+    ExFix.start_session_initiator("defaults", "S", "T", FixEmptySessionHandler, session_registry: CaptureRegistry)
+
+    assert_receive {:start_session, "defaults", config}
+    assert config.hostname == "localhost"
+    assert config.port == 9876
+    assert config.log_incoming_msg == true
+    assert config.transport_mod == :gen_tcp
+  end
+end
diff --git a/test/in_message_test.exs b/test/in_message_test.exs
index 8dc1713..e0c8d0c 100644
--- a/test/in_message_test.exs
+++ b/test/in_message_test.exs
@@ -18,11 +18,14 @@ defmodule ExFix.InMessageTest do
     %{bin_msg: bin_msg}
   end
 
-  test "InMessage tests", %{bin_msg: bin_msg} do
+  test "get_field returns value", %{bin_msg: bin_msg} do
     fix_msg = Parser.parse1(bin_msg, Dictionary, 12_345)
     assert InMessage.get_field(fix_msg, "49") == "MARKET"
     assert InMessage.get_field(fix_msg, "52") == "20161007-16:28:50.802"
+  end
 
-    # assert InMessage.get_field(fix_msg, "SendingTime", TestDict) == Calendar.DateTime.Parse.rfc3339_utc
+  test "get_field returns nil for missing field", %{bin_msg: bin_msg} do
+    fix_msg = Parser.parse1(bin_msg, Dictionary, 12_345)
+    assert InMessage.get_field(fix_msg, "9999") == nil
   end
 end
diff --git a/test/parser_test.exs b/test/parser_test.exs
index 10052ad..2e41c00 100644
--- a/test/parser_test.exs
+++ b/test/parser_test.exs
@@ -124,6 +124,23 @@ defmodule ExFix.ParserTest do
     assert fix_msg.original_fix_msg == data
   end
 
+  test "Parse message with invalid begin string" do
+    data = msg("8=FIX4.2|9=12|10=000|")
+    fix_msg = Parser.parse1(data, Dictionary, 1)
+    assert fix_msg.valid == false
+    assert fix_msg.error_reason == :begin_string_error
+    assert fix_msg.original_fix_msg == data
+  end
+
+  test "Parse message with unexpected seqnum" do
+    now = DateTime.from_naive!(~N[2017-07-17 17:50:56], "Etc/UTC")
+    data = build_message("0", 10, "SENDER", "TARGET", now)
+    fix_msg = Parser.parse1(data, Dictionary, 5)
+    assert fix_msg.valid == false
+    assert fix_msg.error_reason == :unexpected_seqnum
+    assert fix_msg.seqnum == 10
+  end
+
   test "Parse message - stage 1 - subject with 2 fields" do
     data =
       msg(
diff --git a/test/session_sup_test.exs b/test/session_sup_test.exs
new file mode 100644
index 0000000..55cf373
--- /dev/null
+++ b/test/session_sup_test.exs
@@ -0,0 +1,14 @@
+defmodule ExFix.SessionSupTest do
+  use ExUnit.Case
+
+  test "start_link when already started" do
+    assert {:error, {:already_started, _}} = ExFix.SessionSup.start_link([])
+  end
+
+  test "dynamic supervisor can start child" do
+    {:ok, pid} = DynamicSupervisor.start_child(ExFix.SessionSup, {Task, fn -> :timer.sleep(10) end})
+    assert is_pid(pid)
+    ref = Process.monitor(pid)
+    assert_receive {:DOWN, ^ref, :process, ^pid, :normal}, 50
+  end
+end
diff --git a/test/session_worker_failure_test.exs b/test/session_worker_failure_test.exs
new file mode 100644
index 0000000..60c3bce
--- /dev/null
+++ b/test/session_worker_failure_test.exs
@@ -0,0 +1,36 @@
+defmodule ExFix.SessionWorkerFailureTest do
+  use ExUnit.Case
+
+  alias ExFix.SessionConfig
+  alias ExFix.TestHelper.FixEmptySessionHandler
+
+  defmodule FailTransport do
+    def connect(_host, _port, _opts), do: {:error, :econnrefused}
+    def send(_conn, _data), do: :ok
+    def close(_conn), do: :ok
+  end
+
+  alias ExFix.TestHelper.TestSessionRegistry
+
+  test "worker reports reconnecting on connection failure" do
+    Process.flag(:trap_exit, true)
+    {:ok, _} = TestSessionRegistry.start_link()
+    config = %SessionConfig{
+      name: "fail1",
+      mode: :initiator,
+      sender_comp_id: "S",
+      target_comp_id: "T",
+      session_handler: FixEmptySessionHandler,
+      transport_mod: FailTransport,
+      transport_options: [],
+      log_incoming_msg: false,
+      log_outgoing_msg: false,
+      reconnect_interval: 0
+    }
+
+    {:ok, pid} = ExFix.SessionWorker.start_link(config, TestSessionRegistry)
+    ref = Process.monitor(pid)
+    assert_receive {:DOWN, ^ref, :process, ^pid, :econnrefused}
+    assert TestSessionRegistry.get_session_status("fail1") == :reconnecting
+  end
+end
diff --git a/test/session_worker_test.exs b/test/session_worker_test.exs
index 0f463b3..d15ccd2 100644
--- a/test/session_worker_test.exs
+++ b/test/session_worker_test.exs
@@ -145,4 +145,65 @@ defmodule ExFix.SessionWorkerTest do
     SessionWorker.stop("sessiontest1")
     assert TestSessionRegistry.get_session_status("sessiontest1") == :disconnected
   end
+
+  test "higher seqnum triggers resend request" do
+
+    cfg = %SessionConfig{
+      name: "resend_sess",
+      mode: :initiator,
+      sender_comp_id: "SENDER",
+      target_comp_id: "TARGET",
+      session_handler: FixEmptySessionHandler,
+      dictionary: DefaultDictionary,
+      transport_mod: TestTransport,
+      transport_options: [test_pid: self()]
+    }
+
+    {:ok, _pid} = SessionWorker.start_link(cfg, TestSessionRegistry)
+    assert_receive {:data, _logon_msg}
+
+    now = DateTime.utc_now()
+    logon = %MessageToSend{seqnum: 1, sender: "TARGET", orig_sending_time: now, target: "SENDER", msg_type: "A", body: []}
+    TestTransport.receive_data("resend_sess", Serializer.serialize(logon, now))
+    Process.sleep(20)
+
+    msg = %MessageToSend{seqnum: 12, sender: "TARGET", orig_sending_time: now, target: "SENDER", msg_type: "8", body: []}
+    TestTransport.receive_data("resend_sess", Serializer.serialize(msg, now))
+
+    assert_receive {:data, resend}
+    parsed = Parser.parse(resend, DefaultDictionary, 1)
+    assert parsed.msg_type == "2"
+    SessionWorker.stop("resend_sess")
+  end
+
+  test "invalid SenderCompID triggers logout" do
+    cfg = %SessionConfig{
+      name: "badcomp",
+      mode: :initiator,
+      sender_comp_id: "SENDER",
+      target_comp_id: "TARGET",
+      session_handler: FixEmptySessionHandler,
+      dictionary: DefaultDictionary,
+      transport_mod: TestTransport,
+      transport_options: [test_pid: self()]
+    }
+
+    {:ok, pid} = SessionWorker.start_link(cfg, TestSessionRegistry)
+    ref = Process.monitor(pid)
+    assert_receive {:data, _}
+
+    now = DateTime.utc_now()
+    logon = %MessageToSend{seqnum: 1, sender: "TARGET", orig_sending_time: now, target: "SENDER", msg_type: "A", body: []}
+    TestTransport.receive_data("badcomp", Serializer.serialize(logon, now))
+    Process.sleep(20)
+
+    msg = %MessageToSend{seqnum: 2, sender: "OTHER", orig_sending_time: now, target: "SENDER", msg_type: "8", body: []}
+    TestTransport.receive_data("badcomp", Serializer.serialize(msg, now))
+
+    assert_receive {:data, reject}
+    assert_receive {:data, logout}
+    assert Parser.parse(reject, DefaultDictionary, 1).msg_type == "3"
+    assert Parser.parse(logout, DefaultDictionary, 1).msg_type == "5"
+    assert_receive {:DOWN, ^ref, :process, ^pid, :normal}, 1000
+  end
 end