test(api): integration tests for public LoadModel + Generate

Tests: MetalAvailable, DefaultBackend, GetBackend, LoadModel error
paths, options, defaults. Model-dependent test skips when model
not available on disk.

Co-Authored-By: Virgil <virgil@lethean.io>

mlx_test.go

@@ -0,0 +1,123 @@
+//go:build darwin && arm64
+
+package mlx_test
+
+import (
+	"context"
+	"os"
+	"testing"
+
+	"forge.lthn.ai/core/go-mlx"
+)
+
+func TestMetalAvailable(t *testing.T) {
+	if !mlx.MetalAvailable() {
+		t.Fatal("MetalAvailable() = false on darwin/arm64")
+	}
+}
+
+func TestDefaultBackend(t *testing.T) {
+	b, err := mlx.Default()
+	if err != nil {
+		t.Fatalf("Default() error: %v", err)
+	}
+	if b.Name() != "metal" {
+		t.Errorf("Default().Name() = %q, want %q", b.Name(), "metal")
+	}
+}
+
+func TestGetBackend(t *testing.T) {
+	b, ok := mlx.Get("metal")
+	if !ok {
+		t.Fatal("Get(\"metal\") returned false")
+	}
+	if b.Name() != "metal" {
+		t.Errorf("Name() = %q, want %q", b.Name(), "metal")
+	}
+
+	_, ok = mlx.Get("nonexistent")
+	if ok {
+		t.Error("Get(\"nonexistent\") should return false")
+	}
+}
+
+func TestLoadModel_NoBackend(t *testing.T) {
+	_, err := mlx.LoadModel("/nonexistent/path")
+	if err == nil {
+		t.Error("expected error for nonexistent model path")
+	}
+}
+
+func TestLoadModel_WithBackend(t *testing.T) {
+	_, err := mlx.LoadModel("/nonexistent/path", mlx.WithBackend("nonexistent"))
+	if err == nil {
+		t.Error("expected error for nonexistent backend")
+	}
+}
+
+func TestOptions(t *testing.T) {
+	cfg := mlx.ApplyGenerateOpts([]mlx.GenerateOption{
+		mlx.WithMaxTokens(64),
+		mlx.WithTemperature(0.7),
+		mlx.WithTopK(40),
+		mlx.WithTopP(0.9),
+		mlx.WithStopTokens(1, 2, 3),
+	})
+	if cfg.MaxTokens != 64 {
+		t.Errorf("MaxTokens = %d, want 64", cfg.MaxTokens)
+	}
+	if cfg.Temperature != 0.7 {
+		t.Errorf("Temperature = %f, want 0.7", cfg.Temperature)
+	}
+	if cfg.TopK != 40 {
+		t.Errorf("TopK = %d, want 40", cfg.TopK)
+	}
+	if cfg.TopP != 0.9 {
+		t.Errorf("TopP = %f, want 0.9", cfg.TopP)
+	}
+	if len(cfg.StopTokens) != 3 {
+		t.Errorf("StopTokens len = %d, want 3", len(cfg.StopTokens))
+	}
+}
+
+func TestDefaults(t *testing.T) {
+	cfg := mlx.DefaultGenerateConfig()
+	if cfg.MaxTokens != 256 {
+		t.Errorf("default MaxTokens = %d, want 256", cfg.MaxTokens)
+	}
+	if cfg.Temperature != 0.0 {
+		t.Errorf("default Temperature = %f, want 0.0", cfg.Temperature)
+	}
+}
+
+// TestLoadModel_Generate requires a model on disk. Skipped in CI.
+func TestLoadModel_Generate(t *testing.T) {
+	const modelPath = "/Volumes/Data/lem/safetensors/gemma-3/"
+	if _, err := os.Stat(modelPath); err != nil {
+		t.Skip("model not available at", modelPath)
+	}
+
+	m, err := mlx.LoadModel(modelPath)
+	if err != nil {
+		t.Fatalf("LoadModel: %v", err)
+	}
+	defer m.Close()
+
+	if m.ModelType() != "gemma3" {
+		t.Errorf("ModelType() = %q, want %q", m.ModelType(), "gemma3")
+	}
+
+	ctx := context.Background()
+	var count int
+	for tok := range m.Generate(ctx, "What is 2+2?", mlx.WithMaxTokens(16)) {
+		count++
+		t.Logf("[%d] %q", tok.ID, tok.Text)
+	}
+	if err := m.Err(); err != nil {
+		t.Fatalf("Generate error: %v", err)
+	}
+	if count == 0 {
+		t.Error("Generate produced no tokens")
+	}
+	t.Logf("Generated %d tokens", count)
+}