Replay vs Lovable.dev: Which Generates Better Unit Tests from Video in React (2026)?

TL;DR: Replay's behavior-driven approach to code generation from video outperforms Lovable.dev in creating comprehensive and contextually relevant unit tests for React components, leading to higher code quality and maintainability.

The promise of AI-powered code generation is alluring, especially when it comes to the tedious task of writing unit tests. Screenshot-to-code tools have made some inroads, but they often fall short of understanding the intent behind the UI. We're moving beyond static image analysis to dynamic behavior analysis. This is where Replay shines. Today, we're pitting Replay against Lovable.dev, a screenshot-to-code competitor, in generating React unit tests from video recordings. Let's see who delivers more value in 2026.

The Problem with Screenshot-to-Code for Unit Tests#

Screenshot-to-code tools are great for quickly scaffolding UI components. However, unit tests require a deeper understanding of the component's behavior. A screenshot only captures the visual state at a single point in time. It doesn't tell you:

• •How the component responds to user interactions
• •What data transformations occur internally
• •How different states are triggered

This limitation leads to superficial unit tests that only verify the presence of elements, not their functionality. You end up with brittle tests that break easily with minor UI changes and provide little confidence in the application's correctness.

Replay: Behavior-Driven Reconstruction for Smarter Unit Tests#

Replay takes a different approach. Instead of relying on static screenshots, Replay analyzes video recordings of user interactions. This "Behavior-Driven Reconstruction" allows Replay to understand:

• •User flows and interactions
• •State transitions
• •Data dependencies

By understanding the behavior of the UI, Replay can generate unit tests that are more comprehensive, robust, and maintainable. Replay uses Gemini to reconstruct the code, ensuring the generated tests accurately reflect the intended functionality.

Replay vs. Lovable.dev: A Head-to-Head Comparison#

Let's compare Replay and Lovable.dev across key features relevant to unit test generation:

As you can see, Replay's ability to analyze video recordings gives it a significant advantage in understanding the behavior of the UI, which translates to better unit tests.

A Practical Example: Generating Unit Tests for a React Form#

Let's consider a simple React form with two input fields (name and email) and a submit button. We'll record a video of a user filling out the form and submitting it.

Lovable.dev's Approach#

Lovable.dev would generate a component based on a screenshot of the form. The generated unit tests would likely focus on verifying the presence of the input fields and the button.

javascript
// Generated by Lovable.dev (example)
import { render, screen } from '@testing-library/react';
import MyForm from './MyForm';

test('renders the form with name and email input fields', () => {
  render(<MyForm />);
  const nameInput = screen.getByLabelText('Name:');
  const emailInput = screen.getByLabelText('Email:');
  const submitButton = screen.getByRole('button', { name: 'Submit' });

  expect(nameInput).toBeInTheDocument();
  expect(emailInput).toBeInTheDocument();
  expect(submitButton).toBeInTheDocument();
});

This test is a good starting point, but it doesn't verify the actual behavior of the form. It doesn't check if the input fields accept valid data, if the form submission triggers the correct action, or if any error messages are displayed.

Replay's Approach#

Replay, on the other hand, would analyze the video recording and understand the following:

• •The user enters data into the input fields
• •The user clicks the submit button
• •The form submission triggers a specific API call (if applicable)
• •The UI updates based on the API response

Based on this understanding, Replay would generate unit tests that verify these behaviors:

typescript
// Generated by Replay
import { render, screen, fireEvent, waitFor } from '@testing-library/react';
import MyForm from './MyForm';
import { submitForm } from './api'; // Assuming an API call

jest.mock('./api'); // Mock the API call

describe('MyForm', () => {
  it('submits the form with valid data', async () => {
    submitForm.mockResolvedValue({ success: true }); // Mock successful API response

    render(<MyForm />);
    const nameInput = screen.getByLabelText('Name:');
    const emailInput = screen.getByLabelText('Email:');
    const submitButton = screen.getByRole('button', { name: 'Submit' });

    fireEvent.change(nameInput, { target: { value: 'John Doe' } });
    fireEvent.change(emailInput, { target: { value: 'john.doe@example.com' } });
    fireEvent.click(submitButton);

    await waitFor(() => {
      expect(submitForm).toHaveBeenCalledWith({
        name: 'John Doe',
        email: 'john.doe@example.com',
      });
    });

    // Add assertions for UI updates after successful submission (e.g., success message)
  });

  it('displays an error message if the API call fails', async () => {
    submitForm.mockRejectedValue(new Error('API Error')); // Mock failed API response

    render(<MyForm />);
    const nameInput = screen.getByLabelText('Name:');
    const emailInput = screen.getByLabelText('Email:');
    const submitButton = screen.getByRole('button', { name: 'Submit' });

    fireEvent.change(nameInput, { target: { value: 'John Doe' } });
    fireEvent.change(emailInput, { target: { value: 'john.doe@example.com' } });
    fireEvent.click(submitButton);

    await waitFor(() => {
      expect(screen.getByText('Error submitting form')).toBeInTheDocument(); // Assert error message
    });
  });
});

This test suite is more comprehensive because it verifies the entire flow of the form, including data input, form submission, API call, and UI updates based on the API response. This level of detail is only possible because Replay understands the behavior of the UI.

💡 Pro Tip: Replay's Supabase integration allows you to easily mock data and API responses, making your unit tests more reliable and independent of external dependencies.

How Replay Works: A Step-by-Step Guide#

Here's how you can use Replay to generate unit tests from video recordings:

Step 1: Record a Video#

Record a video of yourself interacting with the UI you want to test. Make sure to demonstrate all the key behaviors and state transitions.

Step 2: Upload the Video to Replay#

Upload the video to the Replay platform. Replay will automatically analyze the video and reconstruct the UI.

Step 3: Review and Customize the Generated Code#

Replay will generate the React component code and the corresponding unit tests. Review the generated code and customize it as needed.

📝 Note: Replay provides a visual Product Flow map, allowing you to visualize the user flow and identify potential gaps in your unit tests.

Step 4: Integrate the Unit Tests into Your Project#

Integrate the generated unit tests into your project and run them to ensure that your UI is working as expected.

⚠️ Warning: While Replay generates high-quality unit tests, it's still important to review and customize them to ensure they meet your specific requirements.

The Future of Unit Testing: Behavior-Driven and AI-Powered#

The future of unit testing is behavior-driven and AI-powered. Tools like Replay are paving the way for a new generation of unit tests that are more comprehensive, robust, and maintainable. By understanding the intent behind the UI, we can generate unit tests that provide true confidence in the application's correctness.

Replay's multi-page generation capabilities and style injection further enhance the code's usability, ensuring the generated code seamlessly integrates with your existing project.

Frequently Asked Questions#

Is Replay free to use?#

Replay offers a free tier with limited features and usage. Paid plans are available for more advanced features and higher usage limits.

How is Replay different from v0.dev?#

While both tools generate code, v0.dev primarily focuses on generating UI components from text prompts or design specifications. Replay, on the other hand, focuses on understanding user behavior from video recordings and generating comprehensive unit tests based on that understanding. Replay goes beyond simple UI generation and delves into functional verification.

What frameworks does Replay support?#

Currently, Replay primarily supports React. Support for other frameworks like Vue and Angular is planned for future releases.

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