1 files changed, 54 insertions, 0 deletions
diff --git a/tests/Agent.Core.Tests/LocaleCatalogTests.cs b/tests/Agent.Core.Tests/LocaleCatalogTests.cs
new file mode 100644
index 0000000..e5b6085
--- /dev/null
+++ b/tests/Agent.Core.Tests/LocaleCatalogTests.cs
@@ -0,0 +1,54 @@
+using Agent.Core.Localization;
+
+namespace Agent.Core.Tests;
+
+public sealed class LocaleCatalogTests
+{
+    [Fact]
+    public void MissingSelectedKeyFallsBackToEnglish()
+    {
+        using var directory = new TestDirectory();
+        directory.File("en.json", """{"hello":"Hello {name}","only_en":"fallback"}""");
+        directory.File("ja.json", """{"hello":"こんにちは {name}"}""");
+        LocaleCatalog catalog = LocaleCatalog.Load(directory.Path, "ja");
+        Assert.Equal("fallback", catalog.Get("only_en"));
+        Assert.Equal("こんにちは Codex", catalog.Format("hello", new Dictionary<string, object?> { ["name"] = "Codex" }));
+    }
+
+    [Fact]
+    public void AdditionalLocaleLoadsWithoutCodeChange()
+    {
+        using var directory = new TestDirectory();
+        directory.File("en.json", """{"hello":"Hello"}""");
+        directory.File("zh-CN.json", """{"hello":"你好"}""");
+        Assert.Equal("你好", LocaleCatalog.Load(directory.Path, "zh-CN").Get("hello"));
+    }
+
+    [Theory]
+    [InlineData("{broken")]
+    [InlineData("[]")]
+    public void MalformedLocaleIsFatal(string json)
+    {
+        using var directory = new TestDirectory();
+        directory.File("en.json", json);
+        Assert.Throws<LocaleException>(() => LocaleCatalog.Load(directory.Path, "en"));
+    }
+
+    [Fact]
+    public void UnknownKeyIsFatal()
+    {
+        using var directory = new TestDirectory();
+        directory.File("en.json", """{"known":"value"}""");
+        directory.File("ja.json", """{"known":"値","unknown":"x"}""");
+        Assert.Throws<LocaleException>(() => LocaleCatalog.Load(directory.Path, "ja"));
+    }
+
+    [Fact]
+    public void PlaceholderMismatchIsFatal()
+    {
+        using var directory = new TestDirectory();
+        directory.File("en.json", """{"hello":"Hello {name}"}""");
+        directory.File("ja.json", """{"hello":"こんにちは {user}"}""");
+        Assert.Throws<LocaleException>(() => LocaleCatalog.Load(directory.Path, "ja"));
+    }
+}