Rewrite tests to run without a database

- Unit tests use an in-memory fake database (internal/testutil/fakedb),
  temp folders and httptest; `go test ./...` needs no Docker or env vars
- Integration tests (build tag "integration") start PostgreSQL with
  testcontainers: migrations step by step, SQL dumps (skipped if
  missing) and a full sync against a real database
- Removed tests that only checked copies of the logic or had empty
  bodies, the broken root integration_test.go, compose.test.yaml and
  .env.test with hardcoded paths
- testMusic MP3s replaced with tiny placeholders (sync never decodes
  audio), 194 MB -> 168 KB

internal/server/helpers_test.go

@@ -0,0 +1,120 @@
+package server
+
+import (
+	"context"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"path/filepath"
+	"strings"
+	"sync/atomic"
+	"testing"
+
+	"music-server/internal/config"
+	"music-server/internal/db/repository"
+	"music-server/internal/logging"
+	"music-server/internal/testutil/fakedb"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestMain(m *testing.M) {
+	logging.Init("fatal", false)
+	os.Exit(m.Run())
+}
+
+type fakeDatabase struct {
+	closed  atomic.Bool
+	onClose func()
+}
+
+func (f *fakeDatabase) Health(context.Context) map[string]string {
+	return map[string]string{"status": "up"}
+}
+
+func (f *fakeDatabase) Close() {
+	if f.onClose != nil {
+		f.onClose()
+	}
+	f.closed.Store(true)
+}
+
+// testEnv is a Server backed by an in-memory database and temporary folders.
+type testEnv struct {
+	t       *testing.T
+	cfg     config.Config
+	store   *fakedb.Store
+	db      *fakeDatabase
+	server  *Server
+	handler http.Handler
+}
+
+func writeFile(t *testing.T, path, content string) {
+	t.Helper()
+	require.NoError(t, os.MkdirAll(filepath.Dir(path), 0o755))
+	require.NoError(t, os.WriteFile(path, []byte(content), 0o644))
+}
+
+func newTestEnv(t *testing.T, configure ...func(*config.Config)) *testEnv {
+	t.Helper()
+	base := t.TempDir()
+	cfg := config.Config{
+		Port:               0,
+		MusicPath:          filepath.Join(base, "music"),
+		CharactersPath:     filepath.Join(base, "characters"),
+		SoundCheckPath:     filepath.Join(base, "songs"),
+		FrontendPath:       filepath.Join(base, "frontend"),
+		DisableSessionAuth: true,
+		ReleasesURL:        "http://127.0.0.1:1",
+	}
+	for _, c := range configure {
+		c(&cfg)
+	}
+	writeFile(t, filepath.Join(cfg.CharactersPath, "Adol.png"), "png")
+	writeFile(t, filepath.Join(cfg.CharactersPath, "Aloy.jpg"), "jpg")
+	writeFile(t, filepath.Join(base, "secret.png"), "secret")
+	writeFile(t, filepath.Join(cfg.SoundCheckPath, "check.mp3"), "sound check")
+	writeFile(t, filepath.Join(cfg.FrontendPath, "index.html"), "<html>frontend</html>")
+
+	store := fakedb.New()
+	database := &fakeDatabase{}
+	s, err := New(cfg, store, database)
+	require.NoError(t, err)
+	t.Cleanup(func() { s.sync.Wait(); s.characters.Close() })
+	return &testEnv{t: t, cfg: cfg, store: store, db: database, server: s, handler: s.httpServer.Handler}
+}
+
+// addSong creates a song file and its database rows.
+func (e *testEnv) addSong(soundtrack, song, content string) repository.Song {
+	e.t.Helper()
+	dir := e.cfg.MusicPath + "/" + soundtrack + "/"
+	fileName := song + ".mp3"
+	writeFile(e.t, dir+fileName, content)
+	st, ok := e.store.Soundtrack(soundtrack)
+	if !ok {
+		st = e.store.AddSoundtrack(repository.Soundtrack{SoundtrackName: soundtrack, Path: dir})
+	}
+	return e.store.AddTestSong(repository.Song{SoundtrackID: st.ID, SongName: song, Path: dir + fileName, FileName: &fileName})
+}
+
+func (e *testEnv) do(method, path string, headers ...string) *httptest.ResponseRecorder {
+	return e.doBody(method, path, "", headers...)
+}
+
+func (e *testEnv) doBody(method, path, body string, headers ...string) *httptest.ResponseRecorder {
+	var reader io.Reader
+	if body != "" {
+		reader = strings.NewReader(body)
+	}
+	req := httptest.NewRequest(method, path, reader)
+	if body != "" {
+		req.Header.Set("Content-Type", "application/json")
+	}
+	for i := 0; i+1 < len(headers); i += 2 {
+		req.Header.Set(headers[i], headers[i+1])
+	}
+	rec := httptest.NewRecorder()
+	e.handler.ServeHTTP(rec, req)
+	return rec
+}