chore(vertexai): Add some tests

FUTURE_COPYBARA_INTEGRATE_REVIEW=#14351 from renovate-bot:renovate/main-deps 2e7e530
PiperOrigin-RevId: 895405821

Author: BenjaminKazemi

vertexai/genai/client.go

@@ -459,8 +459,18 @@ func float32pToInt32p(x *float32) *int32 {
 	return &i
 }
 
+func validateClientConfig(cc *genai.ClientConfig) error {
+	if cc != nil && cc.Backend == genai.BackendGeminiAPI {
+		return fmt.Errorf("only Vertex AI backend is supported")
+	}
+	return nil
+}
+
 // NewGenAIClient creates a new Google Vertex AI client and configures the the GenAI components.
 func NewGenAIClient(ctx context.Context, cc *genai.ClientConfig) (*Client, error) {
+	if err := validateClientConfig(cc); err != nil {
+		return nil, err
+	}
 	ac, err := genai.NewInternalAPIClient(ctx, cc)
 	if err != nil {
 		return nil, err

vertexai/genai/client_test.go

@@ -28,6 +28,7 @@ import (
 	"testing"
 
 	"google.golang.org/api/iterator"
+	"google.golang.org/genai"
 )
 
 const defaultModel = "gemini-1.0-pro"
@@ -739,3 +740,40 @@ func printResponse(resp *GenerateContentResponse) {
 	}
 	fmt.Println("---")
 }
+
+func TestNewGenAIClient(t *testing.T) {
+	ctx := context.Background()
+	for _, test := range []struct {
+		name string
+		cc   *genai.ClientConfig
+	}{
+		{name: "nil config", cc: nil},
+		{name: "empty config", cc: &genai.ClientConfig{}},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			client, err := NewGenAIClient(ctx, test.cc)
+			if err != nil {
+				t.Fatalf("NewGenAIClient() failed unexpectedly, err: %v", err)
+			}
+			if client == nil {
+				t.Error("client must not be nil")
+			}
+		})
+	}
+}
+
+func TestNewGenAIClientErrors(t *testing.T) {
+	ctx := context.Background()
+	for _, test := range []struct {
+		name string
+		cc   *genai.ClientConfig
+	}{
+		{name: "gemini backend", cc: &genai.ClientConfig{Backend: genai.BackendGeminiAPI}},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			if _, err := NewGenAIClient(ctx, test.cc); err == nil {
+				t.Error("wants error, but got nil")
+			}
+		})
+	}
+}