1 files changed, 50 insertions, 0 deletions
diff --git a/internal/config/correct_empty_config_test.go b/internal/config/correct_empty_config_test.go
new file mode 100644
index 0000000..27d39da
--- /dev/null
+++ b/internal/config/correct_empty_config_test.go
@@ -0,0 +1,50 @@
+package config
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+// Regression: Load used yaml.Decoder.Decode for KnownFields, which returns
+// io.EOF for an empty or comment-only config.yaml. cmd/thoi treats any non-
+// IsNotExist error as fatal, so an empty config aborted startup instead of
+// booting on defaults (yaml.Unmarshal had returned nil).
+
+func writeEmptyConfig(t *testing.T, body string) string {
+	t.Helper()
+	path := filepath.Join(t.TempDir(), "config.yaml")
+	if err := os.WriteFile(path, []byte(body), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	return path
+}
+
+func TestLoadEmptyFileBootsOnDefaults(t *testing.T) {
+	cfg, err := Load(writeEmptyConfig(t, ""))
+	if err != nil {
+		t.Fatalf("empty config.yaml must load on defaults, got: %v", err)
+	}
+	if cfg.TickLength != Default().TickLength {
+		t.Errorf("TickLength = %d, want default %d", cfg.TickLength, Default().TickLength)
+	}
+	if cfg.Telnet.Port != Default().Telnet.Port {
+		t.Errorf("Telnet.Port = %d, want default %d", cfg.Telnet.Port, Default().Telnet.Port)
+	}
+}
+
+func TestLoadCommentOnlyFileBootsOnDefaults(t *testing.T) {
+	cfg, err := Load(writeEmptyConfig(t, "# nothing configured yet\n\n# ports come from defaults\n"))
+	if err != nil {
+		t.Fatalf("comment-only config.yaml must load on defaults, got: %v", err)
+	}
+	if cfg.StartingRoom != Default().StartingRoom {
+		t.Errorf("StartingRoom = %d, want default %d", cfg.StartingRoom, Default().StartingRoom)
+	}
+}
+
+func TestLoadEmptyFileStillRejectsUnknownKey(t *testing.T) {
+	if _, err := Load(writeEmptyConfig(t, "not_a_real_key: 1\n")); err == nil {
+		t.Fatal("unknown key must still be rejected after the io.EOF fix")
+	}
+}