feat(server/m7-353): coverart.FindSidecar shared helper + tests

internal/coverart/sidecar_test.go

@@ -0,0 +1,54 @@
+package coverart
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestFindSidecar_PrefersCoverJpgOverFolderJpg(t *testing.T) {
+	dir := t.TempDir()
+	must(t, os.WriteFile(filepath.Join(dir, "folder.jpg"), []byte("f"), 0o644))
+	must(t, os.WriteFile(filepath.Join(dir, "cover.jpg"), []byte("c"), 0o644))
+	got := FindSidecar(dir)
+	want := filepath.Join(dir, "cover.jpg")
+	if got != want {
+		t.Errorf("got %q, want %q", got, want)
+	}
+}
+
+func TestFindSidecar_PrefersJpegOverPng(t *testing.T) {
+	dir := t.TempDir()
+	must(t, os.WriteFile(filepath.Join(dir, "cover.png"), []byte("p"), 0o644))
+	must(t, os.WriteFile(filepath.Join(dir, "cover.jpeg"), []byte("j"), 0o644))
+	got := FindSidecar(dir)
+	want := filepath.Join(dir, "cover.jpeg")
+	if got != want {
+		t.Errorf("got %q, want %q", got, want)
+	}
+}
+
+func TestFindSidecar_EmptyDir_ReturnsEmpty(t *testing.T) {
+	dir := t.TempDir()
+	if got := FindSidecar(dir); got != "" {
+		t.Errorf("expected empty string, got %q", got)
+	}
+}
+
+func TestFindSidecar_DirectoryNamedCoverJpg_Skipped(t *testing.T) {
+	dir := t.TempDir()
+	must(t, os.MkdirAll(filepath.Join(dir, "cover.jpg"), 0o755))
+	must(t, os.WriteFile(filepath.Join(dir, "folder.png"), []byte("p"), 0o644))
+	got := FindSidecar(dir)
+	want := filepath.Join(dir, "folder.png")
+	if got != want {
+		t.Errorf("got %q, want %q", got, want)
+	}
+}
+
+func must(t *testing.T, err error) {
+	t.Helper()
+	if err != nil {
+		t.Fatalf("setup: %v", err)
+	}
+}