fix(client): fix label field bug, nil deref, receiver consistency, add tests (#16)

- CreateVoice/EditVoice: write 'labels' field instead of duplicate 'name'
- GetVoice/GetVoices: check http error before dereferencing response
- ConvertSpeechToText*: use value receiver for consistency
- Add Content-Type: application/json header to all JSON POST requests
- Add comprehensive test suite (35+ tests) using httptest

client/client_test.go

@@ -0,0 +1,833 @@
+package client
+
+import (
+	"context"
+	"encoding/json"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"github.com/taigrr/elevenlabs/client/types"
+)
+
+// newTestClient creates a Client pointed at the given test server.
+func newTestClient(ts *httptest.Server) Client {
+	return New("test-api-key").WithEndpoint(ts.URL)
+}
+
+// assertAPIKey checks that the request carries the expected API key header.
+func assertAPIKey(t *testing.T, r *http.Request) {
+	t.Helper()
+	if got := r.Header.Get("xi-api-key"); got != "test-api-key" {
+		t.Errorf("xi-api-key = %q, want %q", got, "test-api-key")
+	}
+}
+
+func TestNew(t *testing.T) {
+	c := New("my-key")
+	if c.apiKey != "my-key" {
+		t.Fatalf("apiKey = %q, want %q", c.apiKey, "my-key")
+	}
+	if c.endpoint != apiEndpoint {
+		t.Fatalf("endpoint = %q, want %q", c.endpoint, apiEndpoint)
+	}
+	if c.httpClient == nil {
+		t.Fatal("httpClient is nil")
+	}
+}
+
+func TestWithEndpoint(t *testing.T) {
+	c := New("k").WithEndpoint("http://custom")
+	if c.endpoint != "http://custom" {
+		t.Fatalf("endpoint = %q", c.endpoint)
+	}
+}
+
+func TestWithAPIKey(t *testing.T) {
+	c := New("old").WithAPIKey("new")
+	if c.apiKey != "new" {
+		t.Fatalf("apiKey = %q", c.apiKey)
+	}
+}
+
+func TestWithHTTPClient(t *testing.T) {
+	custom := &http.Client{}
+	c := New("k").WithHTTPClient(custom)
+	if c.httpClient != custom {
+		t.Fatal("httpClient not set")
+	}
+}
+
+// --- TTS tests ---
+
+func TestTTS(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		assertAPIKey(t, r)
+		if r.Method != http.MethodPost {
+			t.Errorf("method = %s, want POST", r.Method)
+		}
+		if !strings.HasPrefix(r.URL.Path, "/v1/text-to-speech/") {
+			t.Errorf("path = %s", r.URL.Path)
+		}
+		if ct := r.Header.Get("Content-Type"); ct != "application/json" {
+			t.Errorf("Content-Type = %q, want application/json", ct)
+		}
+		var body types.TTS
+		json.NewDecoder(r.Body).Decode(&body)
+		if body.Text != "hello" {
+			t.Errorf("text = %q", body.Text)
+		}
+		w.WriteHeader(200)
+		w.Write([]byte("audio-bytes"))
+	}))
+	defer ts.Close()
+
+	c := newTestClient(ts)
+	data, err := c.TTS(context.Background(), "hello", "voice1", "model1", types.SynthesisOptions{Stability: 0.5, SimilarityBoost: 0.5})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if string(data) != "audio-bytes" {
+		t.Errorf("data = %q", string(data))
+	}
+}
+
+func TestTTSUnauthorized(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(401)
+	}))
+	defer ts.Close()
+
+	c := newTestClient(ts)
+	_, err := c.TTS(context.Background(), "hello", "voice1", "", types.SynthesisOptions{})
+	if err != ErrUnauthorized {
+		t.Fatalf("err = %v, want ErrUnauthorized", err)
+	}
+}
+
+func TestTTSStream(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if !strings.HasSuffix(r.URL.Path, "/stream") {
+			t.Errorf("path = %s, want stream suffix", r.URL.Path)
+		}
+		w.WriteHeader(200)
+		w.Write([]byte("streamed"))
+	}))
+	defer ts.Close()
+
+	c := newTestClient(ts)
+	var buf strings.Builder
+	err := c.TTSStream(context.Background(), &buf, "text", "v1", types.SynthesisOptions{Stability: 0.5, SimilarityBoost: 0.5})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if buf.String() != "streamed" {
+		t.Errorf("got = %q", buf.String())
+	}
+}
+
+func TestTTSWithOptionalParams(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		var body types.TTS
+		json.NewDecoder(r.Body).Decode(&body)
+		if body.PreviousText != "prev" {
+			t.Errorf("previous_text = %q", body.PreviousText)
+		}
+		if body.NextText != "next" {
+			t.Errorf("next_text = %q", body.NextText)
+		}
+		w.WriteHeader(200)
+		w.Write([]byte("ok"))
+	}))
+	defer ts.Close()
+
+	c := newTestClient(ts)
+	_, err := c.TTS(context.Background(), "hello", "v1", "m1",
+		types.SynthesisOptions{Stability: 0.5, SimilarityBoost: 0.5},
+		WithPreviousText("prev"), WithNextText("next"))
+	if err != nil {
+		t.Fatal(err)
+	}
+}
+
+// --- Voice tests ---
+
+func TestGetVoices(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		assertAPIKey(t, r)
+		if r.URL.Path != "/v1/voices" {
+			t.Errorf("path = %s", r.URL.Path)
+		}
+		resp := types.GetVoicesResponseModel{
+			Voices: []types.VoiceResponseModel{
+				{VoiceID: "id1", Name: "Alice"},
+				{VoiceID: "id2", Name: "Bob"},
+			},
+		}
+		json.NewEncoder(w).Encode(resp)
+	}))
+	defer ts.Close()
+
+	c := newTestClient(ts)
+	voices, err := c.GetVoices(context.Background())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(voices) != 2 {
+		t.Fatalf("len = %d", len(voices))
+	}
+	if voices[0].Name != "Alice" {
+		t.Errorf("name = %s", voices[0].Name)
+	}
+}
+
+func TestGetVoiceIDs(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		resp := types.GetVoicesResponseModel{
+			Voices: []types.VoiceResponseModel{
+				{VoiceID: "id1"},
+				{VoiceID: "id2"},
+			},
+		}
+		json.NewEncoder(w).Encode(resp)
+	}))
+	defer ts.Close()
+
+	c := newTestClient(ts)
+	ids, err := c.GetVoiceIDs(context.Background())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(ids) != 2 || ids[0] != "id1" || ids[1] != "id2" {
+		t.Errorf("ids = %v", ids)
+	}
+}
+
+func TestGetVoice(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		assertAPIKey(t, r)
+		if r.URL.Path != "/v1/voices/v123" {
+			t.Errorf("path = %s", r.URL.Path)
+		}
+		resp := types.VoiceResponseModel{VoiceID: "v123", Name: "Test"}
+		json.NewEncoder(w).Encode(resp)
+	}))
+	defer ts.Close()
+
+	c := newTestClient(ts)
+	voice, err := c.GetVoice(context.Background(), "v123")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if voice.VoiceID != "v123" {
+		t.Errorf("voiceID = %s", voice.VoiceID)
+	}
+}
+
+func TestGetVoiceUnauthorized(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(401)
+	}))
+	defer ts.Close()
+
+	c := newTestClient(ts)
+	_, err := c.GetVoice(context.Background(), "v1")
+	if err != ErrUnauthorized {
+		t.Fatalf("err = %v, want ErrUnauthorized", err)
+	}
+}
+
+func TestDeleteVoice(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		assertAPIKey(t, r)
+		if r.Method != http.MethodDelete {
+			t.Errorf("method = %s", r.Method)
+		}
+		w.WriteHeader(200)
+	}))
+	defer ts.Close()
+
+	c := newTestClient(ts)
+	err := c.DeleteVoice(context.Background(), "v1")
+	if err != nil {
+		t.Fatal(err)
+	}
+}
+
+func TestGetVoiceSettings(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		resp := types.SynthesisOptions{Stability: 0.5, SimilarityBoost: 0.8}
+		json.NewEncoder(w).Encode(resp)
+	}))
+	defer ts.Close()
+
+	c := newTestClient(ts)
+	settings, err := c.GetVoiceSettings(context.Background(), "v1")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if settings.Stability != 0.5 {
+		t.Errorf("stability = %f", settings.Stability)
+	}
+}
+
+func TestEditVoiceSettings(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if ct := r.Header.Get("Content-Type"); ct != "application/json" {
+			t.Errorf("Content-Type = %q", ct)
+		}
+		w.WriteHeader(200)
+		json.NewEncoder(w).Encode(types.SynthesisOptions{})
+	}))
+	defer ts.Close()
+
+	c := newTestClient(ts)
+	err := c.EditVoiceSettings(context.Background(), "v1", types.SynthesisOptions{Stability: 0.5})
+	if err != nil {
+		t.Fatal(err)
+	}
+}
+
+// --- User tests ---
+
+func TestGetUserInfo(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		assertAPIKey(t, r)
+		resp := types.UserResponseModel{
+			Subscription: types.Subscription{Tier: "pro"},
+			IsNewUser:    false,
+		}
+		json.NewEncoder(w).Encode(resp)
+	}))
+	defer ts.Close()
+
+	c := newTestClient(ts)
+	info, err := c.GetUserInfo(context.Background())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if info.Subscription.Tier != "pro" {
+		t.Errorf("tier = %s", info.Subscription.Tier)
+	}
+}
+
+func TestGetSubscriptionInfo(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		resp := types.UserResponseModel{
+			Subscription: types.Subscription{Tier: "starter", CharacterLimit: 10000},
+		}
+		json.NewEncoder(w).Encode(resp)
+	}))
+	defer ts.Close()
+
+	c := newTestClient(ts)
+	sub, err := c.GetSubscriptionInfo(context.Background())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if sub.CharacterLimit != 10000 {
+		t.Errorf("limit = %d", sub.CharacterLimit)
+	}
+}
+
+// --- History tests ---
+
+func TestGetHistoryItemList(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		assertAPIKey(t, r)
+		resp := types.GetHistoryResponse{
+			History: []types.HistoryItemList{
+				{HistoryItemID: "h1", VoiceID: "v1", Text: "hello"},
+				{HistoryItemID: "h2", VoiceID: "v2", Text: "world"},
+			},
+		}
+		json.NewEncoder(w).Encode(resp)
+	}))
+	defer ts.Close()
+
+	c := newTestClient(ts)
+	items, err := c.GetHistoryItemList(context.Background())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(items) != 2 {
+		t.Fatalf("len = %d", len(items))
+	}
+}
+
+func TestGetHistoryIDs(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		resp := types.GetHistoryResponse{
+			History: []types.HistoryItemList{
+				{HistoryItemID: "h1", VoiceID: "v1"},
+				{HistoryItemID: "h2", VoiceID: "v2"},
+				{HistoryItemID: "h3", VoiceID: "v1"},
+			},
+		}
+		json.NewEncoder(w).Encode(resp)
+	}))
+	defer ts.Close()
+
+	c := newTestClient(ts)
+
+	// No filter
+	ids, err := c.GetHistoryIDs(context.Background())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(ids) != 3 {
+		t.Errorf("unfiltered len = %d", len(ids))
+	}
+}
+
+func TestGetHistoryIDsFiltered(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		resp := types.GetHistoryResponse{
+			History: []types.HistoryItemList{
+				{HistoryItemID: "h1", VoiceID: "v1"},
+				{HistoryItemID: "h2", VoiceID: "v2"},
+				{HistoryItemID: "h3", VoiceID: "v1"},
+			},
+		}
+		json.NewEncoder(w).Encode(resp)
+	}))
+	defer ts.Close()
+
+	c := newTestClient(ts)
+	ids, err := c.GetHistoryIDs(context.Background(), "v1")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(ids) != 2 {
+		t.Errorf("filtered len = %d, want 2", len(ids))
+	}
+}
+
+func TestHistoryDelete(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.Method != http.MethodDelete {
+			t.Errorf("method = %s", r.Method)
+		}
+		w.WriteHeader(200)
+	}))
+	defer ts.Close()
+
+	c := newTestClient(ts)
+	ok, err := c.HistoryDelete(context.Background(), "h1")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !ok {
+		t.Error("expected true")
+	}
+}
+
+func TestHistoryDownloadAudio(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(200)
+		w.Write([]byte("audio-data"))
+	}))
+	defer ts.Close()
+
+	c := newTestClient(ts)
+	data, err := c.HistoryDownloadAudio(context.Background(), "h1")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(data) == 0 {
+		t.Error("expected non-empty data")
+	}
+}
+
+// --- Samples tests ---
+
+func TestDeleteVoiceSample(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.Method != http.MethodDelete {
+			t.Errorf("method = %s", r.Method)
+		}
+		w.WriteHeader(200)
+	}))
+	defer ts.Close()
+
+	c := newTestClient(ts)
+	ok, err := c.DeleteVoiceSample(context.Background(), "v1", "s1")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !ok {
+		t.Error("expected true")
+	}
+}
+
+func TestDownloadVoiceSample(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(200)
+		w.Write([]byte("sample-audio"))
+	}))
+	defer ts.Close()
+
+	c := newTestClient(ts)
+	data, err := c.DownloadVoiceSample(context.Background(), "v1", "s1")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(data) == 0 {
+		t.Error("expected non-empty data")
+	}
+}
+
+// --- Sound generation tests ---
+
+func TestSoundGeneration(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		assertAPIKey(t, r)
+		if ct := r.Header.Get("Content-Type"); ct != "application/json" {
+			t.Errorf("Content-Type = %q", ct)
+		}
+		var body types.SoundGeneration
+		json.NewDecoder(r.Body).Decode(&body)
+		if body.Text != "thunder" {
+			t.Errorf("text = %q", body.Text)
+		}
+		w.WriteHeader(200)
+		w.Write([]byte("sound-bytes"))
+	}))
+	defer ts.Close()
+
+	c := newTestClient(ts)
+	data, err := c.SoundGeneration(context.Background(), "thunder", 0, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if string(data) != "sound-bytes" {
+		t.Errorf("data = %q", string(data))
+	}
+}
+
+func TestSoundGenerationWriter(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(200)
+		w.Write([]byte("streamed-sound"))
+	}))
+	defer ts.Close()
+
+	c := newTestClient(ts)
+	var buf strings.Builder
+	err := c.SoundGenerationWriter(context.Background(), &buf, "rain", 5.0, 0.5)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if buf.String() != "streamed-sound" {
+		t.Errorf("got = %q", buf.String())
+	}
+}
+
+// --- STT tests ---
+
+func TestConvertSpeechToTextFromReader(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		assertAPIKey(t, r)
+		if r.Method != http.MethodPost {
+			t.Errorf("method = %s", r.Method)
+		}
+		if !strings.HasPrefix(r.Header.Get("Content-Type"), "multipart/form-data") {
+			t.Errorf("Content-Type = %s", r.Header.Get("Content-Type"))
+		}
+		resp := types.SpeechToTextResponse{
+			Text:         "hello world",
+			LanguageCode: "en",
+		}
+		json.NewEncoder(w).Encode(resp)
+	}))
+	defer ts.Close()
+
+	c := newTestClient(ts)
+	resp, err := c.ConvertSpeechToTextFromReader(
+		context.Background(),
+		strings.NewReader("fake-audio"),
+		"test.wav",
+		types.SpeechToTextRequest{ModelID: types.SpeechToTextModelScribeV1},
+	)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if resp.Text != "hello world" {
+		t.Errorf("text = %q", resp.Text)
+	}
+}
+
+func TestConvertSpeechToTextUnauthorized(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(401)
+	}))
+	defer ts.Close()
+
+	c := newTestClient(ts)
+	_, err := c.ConvertSpeechToTextFromReader(
+		context.Background(),
+		strings.NewReader("fake"),
+		"test.wav",
+		types.SpeechToTextRequest{ModelID: types.SpeechToTextModelScribeV1},
+	)
+	if err != ErrUnauthorized {
+		t.Fatalf("err = %v, want ErrUnauthorized", err)
+	}
+}
+
+// --- Types tests ---
+
+func TestSynthesisOptionsClamp(t *testing.T) {
+	tests := []struct {
+		name string
+		in   types.SynthesisOptions
+		want types.SynthesisOptions
+	}{
+		{
+			name: "valid values unchanged",
+			in:   types.SynthesisOptions{Stability: 0.5, SimilarityBoost: 0.8, Style: 0.3},
+			want: types.SynthesisOptions{Stability: 0.5, SimilarityBoost: 0.8, Style: 0.3},
+		},
+		{
+			name: "out of range clamped",
+			in:   types.SynthesisOptions{Stability: 2.0, SimilarityBoost: -1.0, Style: 5.0},
+			want: types.SynthesisOptions{Stability: 0.75, SimilarityBoost: 0.75, Style: 0.0},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			tt.in.Clamp()
+			if tt.in.Stability != tt.want.Stability {
+				t.Errorf("Stability = %f, want %f", tt.in.Stability, tt.want.Stability)
+			}
+			if tt.in.SimilarityBoost != tt.want.SimilarityBoost {
+				t.Errorf("SimilarityBoost = %f, want %f", tt.in.SimilarityBoost, tt.want.SimilarityBoost)
+			}
+			if tt.in.Style != tt.want.Style {
+				t.Errorf("Style = %f, want %f", tt.in.Style, tt.want.Style)
+			}
+		})
+	}
+}
+
+func TestValidationErrorString(t *testing.T) {
+	ve := types.ValidationError{Msg: "bad input", Type_: "value_error"}
+	s := ve.Error()
+	if !strings.Contains(s, "bad input") {
+		t.Errorf("error = %q", s)
+	}
+}
+
+func TestParamErrorString(t *testing.T) {
+	pe := types.ParamError{}
+	pe.Detail.Status = "error"
+	pe.Detail.Message = "invalid param"
+	s := pe.Error()
+	if !strings.Contains(s, "invalid param") {
+		t.Errorf("error = %q", s)
+	}
+}
+
+// --- TTSWriter test ---
+
+func TestTTSWriter(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(200)
+		w.Write([]byte("written-audio"))
+	}))
+	defer ts.Close()
+
+	c := newTestClient(ts)
+	var buf strings.Builder
+	err := c.TTSWriter(context.Background(), &buf, "hello", "m1", "v1", types.SynthesisOptions{Stability: 0.5, SimilarityBoost: 0.5})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if buf.String() != "written-audio" {
+		t.Errorf("got = %q", buf.String())
+	}
+}
+
+// --- DownloadVoiceSampleWriter test ---
+
+func TestDownloadVoiceSampleWriter(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(200)
+		w.Write([]byte("sample-stream"))
+	}))
+	defer ts.Close()
+
+	c := newTestClient(ts)
+	var buf strings.Builder
+	err := c.DownloadVoiceSampleWriter(context.Background(), &buf, "v1", "s1")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if buf.String() != "sample-stream" {
+		t.Errorf("got = %q", buf.String())
+	}
+}
+
+// --- HistoryDownloadAudioWriter test ---
+
+func TestHistoryDownloadAudioWriter(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(200)
+		w.Write([]byte("audio-stream"))
+	}))
+	defer ts.Close()
+
+	c := newTestClient(ts)
+	var buf strings.Builder
+	err := c.HistoryDownloadAudioWriter(context.Background(), &buf, "h1")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if buf.String() != "audio-stream" {
+		t.Errorf("got = %q", buf.String())
+	}
+}
+
+// --- HistoryDownloadZip tests ---
+
+func TestHistoryDownloadZip(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if ct := r.Header.Get("Content-Type"); ct != "application/json" {
+			t.Errorf("Content-Type = %q, want application/json", ct)
+		}
+		var body types.HistoryPost
+		json.NewDecoder(r.Body).Decode(&body)
+		if len(body.HistoryItemIds) < 2 {
+			t.Errorf("expected at least 2 ids, got %d", len(body.HistoryItemIds))
+		}
+		w.WriteHeader(200)
+		w.Write([]byte("zip-data"))
+	}))
+	defer ts.Close()
+
+	c := newTestClient(ts)
+	data, err := c.HistoryDownloadZip(context.Background(), "h1", "h2")
+	if err != nil {
+		t.Fatal(err)
+	}
+	_ = data
+}
+
+func TestHistoryDownloadZipWriter(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(200)
+		w.Write([]byte("zip-stream"))
+	}))
+	defer ts.Close()
+
+	c := newTestClient(ts)
+	var buf strings.Builder
+	err := c.HistoryDownloadZipWriter(context.Background(), &buf, "h1", "h2")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !strings.Contains(buf.String(), "zip-stream") {
+		t.Errorf("got = %q", buf.String())
+	}
+}
+
+// Verify CreateVoice sends multipart with correct field names
+func TestCreateVoiceFieldNames(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		assertAPIKey(t, r)
+		if err := r.ParseMultipartForm(1 << 20); err != nil {
+			t.Fatal(err)
+		}
+		name := r.FormValue("name")
+		if name != "TestVoice" {
+			t.Errorf("name = %q", name)
+		}
+		labels := r.FormValue("labels")
+		if labels != "english, male" {
+			t.Errorf("labels = %q, want %q", labels, "english, male")
+		}
+		w.WriteHeader(200)
+	}))
+	defer ts.Close()
+
+	c := newTestClient(ts)
+	err := c.CreateVoice(context.Background(), "TestVoice", "A test voice", []string{"english", "male"}, nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+}
+
+// Verify handling of 422 validation errors
+func TestTTS422(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(422)
+		json.NewEncoder(w).Encode(types.ValidationError{Msg: "invalid", Type_: "value_error"})
+	}))
+	defer ts.Close()
+
+	c := newTestClient(ts)
+	_, err := c.TTS(context.Background(), "hello", "v1", "", types.SynthesisOptions{})
+	if err == nil {
+		t.Fatal("expected error")
+	}
+	if !strings.Contains(err.Error(), "invalid") {
+		t.Errorf("error = %q", err.Error())
+	}
+}
+
+// Test that STT properly sends diarize and other fields
+func TestSTTFields(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if err := r.ParseMultipartForm(1 << 20); err != nil {
+			t.Fatal(err)
+		}
+		if r.FormValue("model_id") != "scribe_v1" {
+			t.Errorf("model_id = %q", r.FormValue("model_id"))
+		}
+		if r.FormValue("diarize") != "true" {
+			t.Errorf("diarize = %q", r.FormValue("diarize"))
+		}
+		if r.FormValue("language_code") != "en" {
+			t.Errorf("language_code = %q", r.FormValue("language_code"))
+		}
+		resp := types.SpeechToTextResponse{Text: "ok"}
+		json.NewEncoder(w).Encode(resp)
+	}))
+	defer ts.Close()
+
+	c := newTestClient(ts)
+	_, err := c.ConvertSpeechToTextFromReader(
+		context.Background(),
+		strings.NewReader("audio"),
+		"test.wav",
+		types.SpeechToTextRequest{
+			ModelID:      types.SpeechToTextModelScribeV1,
+			LanguageCode: "en",
+			Diarize:      true,
+		},
+	)
+	if err != nil {
+		t.Fatal(err)
+	}
+}
+
+// Test that io.Writer variants correctly proxy
+func TestDownloadVoiceSampleWriterProxy(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(200)
+		_, _ = io.WriteString(w, "proxy-test")
+	}))
+	defer ts.Close()
+
+	c := newTestClient(ts)
+	var buf strings.Builder
+	err := c.DownloadVoiceSampleWriter(context.Background(), &buf, "v1", "s1")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if buf.String() != "proxy-test" {
+		t.Errorf("got = %q", buf.String())
+	}
+}

client/history.go

@@ -60,6 +60,7 @@ func (c Client) HistoryDownloadZipWriter(ctx context.Context, w io.Writer, id1,
 		return err
 	}
 
+	req.Header.Set("Content-Type", "application/json")
 	req.Header.Set("accept", "archive/zip")
 	req.Header.Set("xi-api-key", c.apiKey)
 	req.Header.Set("User-Agent", "github.com/taigrr/elevenlabs")
@@ -103,6 +104,7 @@ func (c Client) HistoryDownloadZip(ctx context.Context, id1, id2 string, additio
 		return []byte{}, err
 	}
 
+	req.Header.Set("Content-Type", "application/json")
 	req.Header.Set("accept", "archive/zip")
 	req.Header.Set("xi-api-key", c.apiKey)
 	req.Header.Set("User-Agent", "github.com/taigrr/elevenlabs")

client/sound_gen.go

@@ -78,6 +78,7 @@ func (c Client) requestSoundGeneration(ctx context.Context, params types.SoundGe
 		return nil, err
 	}
 
+	req.Header.Set("Content-Type", "application/json")
 	req.Header.Set("xi-api-key", c.apiKey)
 	req.Header.Set("User-Agent", "github.com/taigrr/elevenlabs")
 	req.Header.Set("accept", "audio/mpeg")

client/stt.go

@@ -16,7 +16,7 @@ import (
 )
 
 // ConvertSpeechToText converts audio to text using the specified file path
-func (c *Client) ConvertSpeechToText(ctx context.Context, audioFilePath string, request types.SpeechToTextRequest) (*types.SpeechToTextResponse, error) {
+func (c Client) ConvertSpeechToText(ctx context.Context, audioFilePath string, request types.SpeechToTextRequest) (*types.SpeechToTextResponse, error) {
 	file, err := os.Open(audioFilePath)
 	if err != nil {
 		return nil, fmt.Errorf("failed to open audio file: %w", err)
@@ -27,7 +27,7 @@ func (c *Client) ConvertSpeechToText(ctx context.Context, audioFilePath string,
 }
 
 // ConvertSpeechToTextFromReader converts audio to text using the provided reader
-func (c *Client) ConvertSpeechToTextFromReader(ctx context.Context, reader io.Reader, filename string, request types.SpeechToTextRequest) (*types.SpeechToTextResponse, error) {
+func (c Client) ConvertSpeechToTextFromReader(ctx context.Context, reader io.Reader, filename string, request types.SpeechToTextRequest) (*types.SpeechToTextResponse, error) {
 	body := &bytes.Buffer{}
 	writer := multipart.NewWriter(body)
 

client/tts.go

@@ -93,6 +93,7 @@ func (c Client) requestTTS(ctx context.Context, params types.TTS, options types.
 	if err != nil {
 		return nil, err
 	}
+	req.Header.Set("Content-Type", "application/json")
 	req.Header.Set("xi-api-key", c.apiKey)
 	req.Header.Set("User-Agent", "github.com/taigrr/elevenlabs")
 	req.Header.Set("accept", "audio/mpeg")

client/voices.go

@@ -31,7 +31,7 @@ func (c Client) CreateVoice(ctx context.Context, name, description string, label
 	}
 	w.WriteField("name", name)
 	w.WriteField("description", description)
-	w.WriteField("name", strings.Join(labels, ", "))
+	w.WriteField("labels", strings.Join(labels, ", "))
 	w.Close()
 	req, err := http.NewRequestWithContext(ctx, http.MethodPost, url, &b)
 	if err != nil {
@@ -107,6 +107,7 @@ func (c Client) EditVoiceSettings(ctx context.Context, voiceID string, settings
 	if err != nil {
 		return err
 	}
+	req.Header.Set("Content-Type", "application/json")
 	req.Header.Set("xi-api-key", c.apiKey)
 	req.Header.Set("User-Agent", "github.com/taigrr/elevenlabs")
 	req.Header.Set("accept", "application/json")
@@ -157,7 +158,7 @@ func (c Client) EditVoice(ctx context.Context, voiceID, name, description string
 	}
 	w.WriteField("name", name)
 	w.WriteField("description", description)
-	w.WriteField("name", strings.Join(labels, ", "))
+	w.WriteField("labels", strings.Join(labels, ", "))
 	w.Close()
 	req, err := http.NewRequestWithContext(ctx, http.MethodPost, url, &b)
 	if err != nil {
@@ -242,14 +243,13 @@ func (c Client) GetVoice(ctx context.Context, voiceID string) (types.VoiceRespon
 	req.Header.Set("User-Agent", "github.com/taigrr/elevenlabs")
 	req.Header.Set("accept", "application/json")
 	res, err := c.httpClient.Do(req)
+	if err != nil {
+		return types.VoiceResponseModel{}, err
+	}
 	switch res.StatusCode {
 	case 401:
 		return types.VoiceResponseModel{}, ErrUnauthorized
 	case 200:
-		if err != nil {
-			return types.VoiceResponseModel{}, err
-		}
-
 		vrm := types.VoiceResponseModel{}
 		defer res.Body.Close()
 		jerr := json.NewDecoder(res.Body).Decode(&vrm)
@@ -284,13 +284,13 @@ func (c Client) GetVoices(ctx context.Context) ([]types.VoiceResponseModel, erro
 	req.Header.Set("User-Agent", "github.com/taigrr/elevenlabs")
 	req.Header.Set("accept", "application/json")
 	res, err := c.httpClient.Do(req)
+	if err != nil {
+		return []types.VoiceResponseModel{}, err
+	}
 	switch res.StatusCode {
 	case 401:
 		return []types.VoiceResponseModel{}, ErrUnauthorized
 	case 200:
-		if err != nil {
-			return []types.VoiceResponseModel{}, err
-		}
 		vr := types.GetVoicesResponseModel{}
 		defer res.Body.Close()
 		jerr := json.NewDecoder(res.Body).Decode(&vr)