Allow the time to be mocked in tests

config/test.exs

@@ -19,4 +19,6 @@ config :logger, level: :warning
 # Initialize plugs at runtime for faster test compilation
 config :phoenix, :plug_init_mode, :runtime
 
-config :chronoscope, Chronoscope.NTS, behaviour: Chronoscope.NTS.BehaviourMock
+config :chronoscope, Chronoscope.NTS,
+  behaviour: Chronoscope.NTS.BehaviourMock,
+  datetime: Chronoscope.NTS.DateTimeMock

lib/chronoscope/nts/certificate.ex

@@ -20,7 +20,7 @@ defmodule Chronoscope.NTS.Certificate do
 
   defp short_year_to_full_year(short_year) do
     {century, current_year} =
-      DateTime.utc_now().year
+      datetime().utc_now().year
       |> to_string()
       |> String.split_at(-2)
 
@@ -32,4 +32,8 @@ defmodule Chronoscope.NTS.Certificate do
       |> then(&"#{&1 + 1}#{short_year}")
     end
   end
+
+  defp datetime() do
+    Application.get_env(:chronoscope, Chronoscope.NTS)[:datetime] || DateTime
+  end
 end

test/chronoscope/nts/certificate_test.exs

@@ -2,8 +2,14 @@ defmodule Chronoscope.NTS.CertificateTest do
   use ExUnit.Case
 
   import Chronoscope.NTS.Certificate
+  import Mox
+
+  setup :verify_on_exit!
 
   test "parses the expiration date of a certificate" do
+    Chronoscope.NTS.DateTimeMock
+    |> stub(:utc_now, &DateTime.utc_now/0)
+
     {:ok, expiration, _} =
       :secp256r1
       |> X509.PrivateKey.new_ec()
@@ -15,12 +21,24 @@ defmodule Chronoscope.NTS.CertificateTest do
     assert DateTime.diff(expiration, DateTime.utc_now(), :day) == 12
   end
 
-  # todo - mock current time
   test "converts certificate datetime to iso8601" do
+    Chronoscope.NTS.DateTimeMock
+    |> expect(:utc_now, fn -> ~U[2024-03-31 01:23:45Z] end)
+
     assert cert_time_to_iso8601("240326110000Z") == "2024-03-26T11:00:00Z"
   end
 
   test "handles century rollover" do
+    Chronoscope.NTS.DateTimeMock
+    |> expect(:utc_now, fn -> ~U[2024-03-31 01:23:45Z] end)
+
     assert cert_time_to_iso8601("010326110000Z") == "2101-03-26T11:00:00Z"
   end
+
+  test "handles millenium rollover" do
+    Chronoscope.NTS.DateTimeMock
+    |> expect(:utc_now, fn -> ~U[2999-03-31 01:23:45Z] end)
+
+    assert cert_time_to_iso8601("010326110000Z") == "3001-03-26T11:00:00Z"
+  end
 end

test/support/mocks.ex

@@ -1 +1,6 @@
+defmodule DateTime.Behaviour do
+  @callback utc_now :: DateTime.t()
+end
+
 Mox.defmock(Chronoscope.NTS.BehaviourMock, for: Chronoscope.NTS.Behaviour)
+Mox.defmock(Chronoscope.NTS.DateTimeMock, for: DateTime.Behaviour)