M3: add unit tests for config resolution and cryptsetup helpers

Tests cover: alias resolution (exact match, device path match, unknown,
empty methods default), AliasFor lookup, Load with missing/valid YAML,
MapperName generation, and token plugin directory detection.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

internal/cryptsetup/cryptsetup_test.go

@@ -0,0 +1,48 @@
+package cryptsetup
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestMapperName(t *testing.T) {
+	tests := []struct {
+		input string
+		want  string
+	}{
+		{"/dev/sda1", "arca-sda1"},
+		{"/dev/nvme0n1p2", "arca-nvme0n1p2"},
+		{"/dev/dm-0", "arca-dm-0"},
+		{"sda1", "arca-sda1"},
+	}
+	for _, tt := range tests {
+		got := MapperName(tt.input)
+		if got != tt.want {
+			t.Errorf("MapperName(%q) = %q, want %q", tt.input, got, tt.want)
+		}
+	}
+}
+
+func TestHasTokenPlugins_WithPlugins(t *testing.T) {
+	tmp := t.TempDir()
+	os.WriteFile(filepath.Join(tmp, "libcryptsetup-token-systemd-fido2.so"), []byte("fake"), 0o644)
+
+	if !hasTokenPlugins(tmp) {
+		t.Error("hasTokenPlugins returned false for dir with plugin")
+	}
+}
+
+func TestHasTokenPlugins_EmptyDir(t *testing.T) {
+	tmp := t.TempDir()
+
+	if hasTokenPlugins(tmp) {
+		t.Error("hasTokenPlugins returned true for empty dir")
+	}
+}
+
+func TestHasTokenPlugins_NonexistentDir(t *testing.T) {
+	if hasTokenPlugins("/nonexistent/path") {
+		t.Error("hasTokenPlugins returned true for nonexistent dir")
+	}
+}