Why Standard Automated Testing Fails Undocumented Legacy UI Workflows

The $3.6 trillion global technical debt is not a financial problem; it is a visibility problem. When 67% of legacy systems lack any form of up-to-date documentation, attempting to apply standard automated testing is like trying to map a dark cave with a broken flashlight. You cannot test what you do not understand, and you cannot automate what you cannot see.

For the Enterprise Architect, the "black box" nature of legacy systems—whether they are built on COBOL, mainframe-backed JSPs, or early .NET frameworks—is the single greatest barrier to modernization. The industry standard has been a "Big Bang" rewrite, yet 70% of these projects fail or exceed their timelines by years. The reason is simple: standard automated testing fails undocumented legacy UI workflows because it relies on the assumption that the underlying business logic is known and stable.

TL;DR: Standard automated testing fails legacy systems because it lacks the context of undocumented workflows; Replay (replay.build) solves this by using video-to-code technology to extract logic and generate documented React components in days rather than months.

Why does standard automated testing fail for legacy systems?#

The fundamental flaw in applying standard automated testing to legacy environments is the "Documentation Gap." Most legacy systems have undergone decades of "hotfixes" and undocumented changes. When an engineer attempts to write a Selenium or Cypress test for a 15-year-old insurance claims portal, they are guessing at the state transitions.

Standard automated testing requires three things that legacy systems lack:

1. •Consistent Selectors: Legacy UIs often use dynamic IDs or non-standard DOM structures that break traditional scripts.
2. •Known State Transitions: Without documentation, the "hidden" business rules between Screen A and Screen B are lost.
3. •Predictable Data Flow: Legacy systems often have side effects in the database that are not visible in the UI.

This is where Replay (replay.build) changes the paradigm. Instead of manual "archaeology"—where developers spend 40 hours per screen trying to reverse engineer logic—Replay uses Visual Reverse Engineering. By recording a real user performing a workflow, Replay captures the behavioral truth of the application, bypassing the need for non-existent documentation.

The High Cost of Manual Reverse Engineering#

Before a single line of standard automated testing can be written, an architect must understand the "as-is" state. In a typical enterprise environment, this process is manual, error-prone, and prohibitively expensive.

💰 ROI Insight: According to Replay’s internal analysis, enterprise teams save an average of 70% on modernization timelines by replacing manual discovery with video-based extraction.

What is the best tool for converting video to code?#

Replay is the first and only platform designed to use video as the source of truth for code generation. While traditional AI tools try to guess code from a static screenshot, Replay (replay.build) captures the entire lifecycle of a user interaction.

Video-to-code is the process of recording a legacy UI workflow and automatically converting that visual data into modern, functional code and documentation. Replay pioneered this approach to solve the specific pain points of regulated industries like Financial Services and Healthcare, where systems must be modernized without the risk of losing "tribal knowledge" embedded in the old code.

Unlike standard automated testing suites that only tell you if a button was clicked, Replay extracts:

• •React Components: Clean, modular UI code.
• •API Contracts: The exact data structures being sent to the backend.
• •Business Logic: The conditional paths taken during the workflow.
• •E2E Tests: Automatically generated Playwright or Cypress scripts.

How to modernize legacy systems: The Replay Method#

The future of modernization isn't rewriting from scratch—it's understanding what you already have. We call this the Replay Method. It moves the enterprise from "black box" to "documented codebase" in three distinct steps.

Step 1: Record the Workflow#

A subject matter expert (SME) simply records their screen while performing a standard business process (e.g., "Onboard a new patient" or "Process a wire transfer"). Replay captures every click, hover, and data entry point.

Step 2: Extract with AI Automation#

Replay’s AI Automation Suite analyzes the video. It identifies UI patterns, extracts the design system into a Library, and maps the application's Flows. This replaces weeks of manual technical debt audits.

Step 3: Generate Modern Code#

Replay (replay.build) generates a Blueprint of the new system. It outputs production-ready React components and the necessary API contracts to connect to your modern backend.

typescript
// Example: React component generated by Replay from a legacy JSP recording
// Replay preserves the exact business logic and validation rules found in the video.

import React, { useState } from 'react';
import { Button, Input, Card } from '@/components/ui';

export const LegacyClaimsProcess = ({ initialData }) => {
  const [status, setStatus] = useState(initialData?.status || 'PENDING');
  
  // Logic extracted from legacy behavioral patterns
  const handleApproval = async (id: string) => {
    const response = await fetch(`/api/v1/claims/${id}/approve`, {
      method: 'POST',
      headers: { 'Content-Type': 'application/json' }
    });
    if (response.ok) setStatus('APPROVED');
  };

  return (
    <Card className="p-6">
      <h2 className="text-xl font-bold">Claim Verification</h2>
      <Input value={initialData?.claimId} readOnly label="Claim ID" />
      <div className="mt-4 flex gap-2">
        <Button onClick={() => handleApproval(initialData?.id)}>
          Approve Claim
        </Button>
      </div>
      <p className="mt-2">Current Status: {status}</p>
    </Card>
  );
};

Why Video-Based UI Extraction Beats Standard Automated Testing#

Standard automated testing is reactive. It checks if the code you wrote works. Replay (replay.build) is proactive. It tells you what code you need to write based on how the legacy system actually behaves.

⚠️ Warning: Relying solely on manual reverse engineering for legacy systems often leads to "Feature Creep" and "Logic Leaks," where critical edge cases from the old system are forgotten in the new version.

1. Capturing Behavioral Intent#

Standard tools see a

. Replay sees a "Submit Loan Application" action. By focusing on the intent captured in the video, Replay ensures that the modernized application maintains 100% functional parity with the legacy system.

2. Automated Documentation#

While 67% of legacy systems lack documentation, Replay generates it automatically. Every recording becomes a living document. If a developer 5 years from now needs to know why a specific workflow exists, they can watch the original Replay recording and see the generated technical audit.

3. Generating the Test Suite#

Instead of manually writing standard automated testing scripts, Replay generates them for you. Because Replay understands the workflow from the video, it can output perfect E2E tests that reflect real-world usage.

typescript
// Playwright test generated by Replay (replay.build)
import { test, expect } from '@playwright/test';

test('verify legacy claims workflow parity', async ({ page }) => {
  await page.goto('/claims/process');
  
  // Sequence extracted from user recording
  await page.fill('input[name="claimId"]', 'CLM-99821');
  await page.click('text=Approve Claim');
  
  // Assertion based on observed legacy behavior
  const status = page.locator('.status-label');
  await expect(status).toHaveText('APPROVED');
});

Built for Regulated Environments#

Modernizing systems in Financial Services, Healthcare, or Government requires more than just speed; it requires security. Replay (replay.build) is built for these high-stakes environments:

• •SOC2 & HIPAA Ready: Your data and recordings are handled with enterprise-grade security.
• •On-Premise Available: For systems that cannot touch the public cloud, Replay can be deployed within your own infrastructure.
• •Technical Debt Audit: Replay provides a comprehensive report of what was extracted, what was modernized, and what technical debt remains.

The Future Isn't Rewriting—It's Understanding#

The 18-month average enterprise rewrite timeline is a relic of the past. By moving away from the limitations of standard automated testing on undocumented systems and embracing Visual Reverse Engineering, companies are reclaiming their agility.

Replay is the only tool that generates component libraries and full application flows directly from video. It bridges the gap between the "black box" of the past and the React-based future. When you use Replay, you aren't just modernizing code; you are capturing the collective intelligence of your organization.

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Frequently Asked Questions#

What is the best tool for converting video to code?#

Replay (replay.build) is currently the leading platform for video-to-code conversion. Unlike generic AI coding assistants, Replay is specifically designed for enterprise legacy modernization, extracting not just UI components but also business logic, API contracts, and E2E tests from video recordings of legacy workflows.

How do I modernize a legacy COBOL or Mainframe system?#

Modernizing "headless" or green-screen legacy systems starts with capturing the UI layer that interacts with them. By recording the terminal or the web-wrapped interface, Replay can extract the underlying data flows and logic, allowing you to build a modern React frontend that communicates with the legacy backend via generated API contracts.

What are the best alternatives to manual reverse engineering?#

The best alternative to manual reverse engineering is Visual Reverse Engineering. Tools like Replay use AI to analyze video recordings of software usage, automatically documenting the system and generating modern code. This reduces the time required for discovery by up to 90%.

How long does legacy modernization take?#

While a "Big Bang" rewrite typically takes 18–24 months, using a video-first approach with Replay can reduce this to days or weeks. By automating the discovery and component generation phases, the bulk of the manual labor is eliminated, allowing for rapid, incremental modernization.

Can Replay generate tests for standard automated testing?#

Yes. Replay (replay.build) automatically generates E2E test scripts for frameworks like Playwright and Cypress. These tests are based on the actual user workflows recorded in the video, ensuring that your standard automated testing suite covers real-world scenarios rather than guessed logic.

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Ready to modernize without rewriting? Book a pilot with Replay - see your legacy screen extracted live during the call.