diff --git a/internal/subsonic/types_test.go b/internal/subsonic/types_test.go
new file mode 100644
index 00000000..4ba10664
--- /dev/null
+++ b/internal/subsonic/types_test.go
@@ -0,0 +1,129 @@
+package subsonic
+
+import (
+	"testing"
+	"time"
+
+	"github.com/jackc/pgx/v5/pgtype"
+)
+
+func TestUUIDRoundTrip(t *testing.T) {
+	cases := []string{
+		"6ba7b810-9dad-11d1-80b4-00c04fd430c8",
+		"00000000-0000-0000-0000-000000000001",
+	}
+	for _, in := range cases {
+		u, ok := parseUUID(in)
+		if !ok {
+			t.Fatalf("parseUUID(%q) failed", in)
+		}
+		if got := uuidToID(u); got != in {
+			t.Errorf("uuidToID(parseUUID(%q)) = %q", in, got)
+		}
+	}
+}
+
+func TestUUIDToIDZero(t *testing.T) {
+	var u pgtype.UUID
+	if got := uuidToID(u); got != "" {
+		t.Errorf("zero uuid → %q, want empty", got)
+	}
+}
+
+func TestParseUUIDInvalid(t *testing.T) {
+	for _, in := range []string{"", "not-a-uuid", "xxx"} {
+		if _, ok := parseUUID(in); ok {
+			t.Errorf("parseUUID(%q) unexpectedly ok", in)
+		}
+	}
+}
+
+func TestIndexLetter(t *testing.T) {
+	cases := map[string]string{
+		"Radiohead":     "R",
+		"the beatles":   "T",
+		"  massive":     "M",
+		"4 Non Blondes": "#",
+		"":              "?",
+		"*NSYNC":        "?",
+		"Éowyn":         "?",
+	}
+	for in, want := range cases {
+		if got := indexLetter(in); got != want {
+			t.Errorf("indexLetter(%q) = %q, want %q", in, got, want)
+		}
+	}
+}
+
+func TestContentTypeForFormat(t *testing.T) {
+	cases := map[string]string{
+		"mp3":     "audio/mpeg",
+		"MP3":     "audio/mpeg",
+		"flac":    "audio/flac",
+		"ogg":     "audio/ogg",
+		"oga":     "audio/ogg",
+		"opus":    "audio/opus",
+		"m4a":     "audio/mp4",
+		"aac":     "audio/mp4",
+		"wav":     "audio/wav",
+		"unknown": "application/octet-stream",
+	}
+	for in, want := range cases {
+		if got := contentTypeForFormat(in); got != want {
+			t.Errorf("contentTypeForFormat(%q) = %q, want %q", in, got, want)
+		}
+	}
+}
+
+func TestYearFromDate(t *testing.T) {
+	d := pgtype.Date{Valid: true, Time: time.Date(1997, 6, 16, 0, 0, 0, 0, time.UTC)}
+	if got := yearFromDate(d); got != 1997 {
+		t.Errorf("yearFromDate = %d", got)
+	}
+	if got := yearFromDate(pgtype.Date{}); got != 0 {
+		t.Errorf("yearFromDate(zero) = %d, want 0", got)
+	}
+}
+
+func TestTimestamptzToRFC3339(t *testing.T) {
+	ts := pgtype.Timestamptz{
+		Valid: true,
+		Time:  time.Date(2026, 1, 2, 3, 4, 5, 0, time.UTC),
+	}
+	if got := timestamptzToRFC3339(ts); got != "2026-01-02T03:04:05Z" {
+		t.Errorf("rfc3339 = %q", got)
+	}
+	if got := timestamptzToRFC3339(pgtype.Timestamptz{}); got != "" {
+		t.Errorf("rfc3339(zero) = %q, want empty", got)
+	}
+}
+
+func TestAtoiDefault(t *testing.T) {
+	cases := []struct {
+		in   string
+		def  int
+		want int
+	}{
+		{"", 7, 7},
+		{"42", 0, 42},
+		{"  12 ", 0, 12},
+		{"junk", 99, 99},
+	}
+	for _, c := range cases {
+		if got := atoiDefault(c.in, c.def); got != c.want {
+			t.Errorf("atoiDefault(%q,%d) = %d, want %d", c.in, c.def, got, c.want)
+		}
+	}
+}
+
+func TestClampInt(t *testing.T) {
+	if got := clampInt(5, 1, 10); got != 5 {
+		t.Errorf("in-range = %d", got)
+	}
+	if got := clampInt(-3, 1, 10); got != 1 {
+		t.Errorf("below = %d", got)
+	}
+	if got := clampInt(99, 1, 10); got != 10 {
+		t.Errorf("above = %d", got)
+	}
+}