oneshot

test/rsh26pool/jst_test.exs

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+defmodule Rsh26pool.JSTTest do
+  use ExUnit.Case, async: true
+
+  alias Rsh26pool.JST
+
+  describe "parse_local/1" do
+    test "interprets the input as wall-clock JST and returns UTC (-9h)" do
+      assert JST.parse_local("2026-07-04T18:00") == {:ok, ~U[2026-07-04 09:00:00Z]}
+    end
+
+    test "accepts a value that already carries seconds" do
+      assert JST.parse_local("2026-07-04T18:00:30") == {:ok, ~U[2026-07-04 09:00:30Z]}
+    end
+
+    test "shifts across the date boundary when JST wall time is early morning" do
+      # 2026-07-04 05:00 JST is the previous UTC day at 20:00.
+      assert JST.parse_local("2026-07-04T05:00") == {:ok, ~U[2026-07-03 20:00:00Z]}
+    end
+
+    test "returns :error on unparseable text" do
+      assert JST.parse_local("garbage") == :error
+    end
+
+    test "returns :error for non-binary input" do
+      assert JST.parse_local(nil) == :error
+      assert JST.parse_local(1234) == :error
+    end
+  end
+
+  describe "to_local/1 and format/1" do
+    test "to_local shifts a stored UTC datetime forward by 9 hours" do
+      assert JST.to_local(~U[2026-07-04 09:00:00Z]) == ~U[2026-07-04 18:00:00Z]
+    end
+
+    test "format renders the stored UTC datetime as JST wall time" do
+      assert JST.format(~U[2026-07-04 09:00:00Z]) == "2026/07/04 18:00"
+    end
+
+    test "format(nil) is the empty string" do
+      assert JST.format(nil) == ""
+    end
+  end
+
+  describe "parse_local |> format round-trip" do
+    test "is the identity on the wall clock at minute precision" do
+      wall_times = [
+        "2026-07-04T18:00",
+        "2026-01-01T00:00",
+        "2026-12-31T23:59",
+        "2026-03-15T09:05",
+        "2026-07-04T05:00"
+      ]
+
+      for wall <- wall_times do
+        assert {:ok, utc} = JST.parse_local(wall)
+        expected = wall |> String.replace("-", "/") |> String.replace("T", " ")
+        assert JST.format(utc) == expected
+      end
+    end
+  end
+end