If you're new to QA — or you're a developer who's been asked to "write some test cases" or "file a bug report" — the distinction between these two documents can be confusing. They look similar. They both describe software behavior. But they serve completely different purposes in the development lifecycle.

Here's a clear breakdown of what each is, when to use each, and how modern tools can generate both automatically.

What Is a Bug Report?

A bug report documents something that went wrong. It describes observed behavior that differs from expected behavior — a defect, an error, an unexpected result.

Bug reports are reactive: you find a bug while testing or using the software, then document what happened.

A complete bug report includes:

Summary — one-sentence description of the problem
Steps to reproduce — the exact actions that trigger the bug
Expected result — what should have happened
Actual result — what actually happened
Severity — how bad is it (Critical/High/Medium/Low)
Environment — browser, OS, version, URL
Evidence — screenshots, GIFs, console errors, network logs

Bug reports answer: "What broke?"

What Is a Test Case?

A test case documents how to verify that a feature works correctly. It's a structured script that someone (or an automated system) follows to confirm expected behavior.

Test cases are proactive: you write them before or during development to define what "correct" looks like.

A complete test case includes:

Test case ID and title — unique identifier and descriptive name
Preconditions — what must be true before the test starts
Test steps — numbered actions to perform
Expected results — what should happen at each step
Priority — High/Medium/Low based on feature importance

Test cases answer: "Does this work correctly?"

The Key Differences

| | Bug Report | Test Case | |---|---|---| | Purpose | Document a defect | Verify expected behavior | | When created | After finding a bug | Before/during development | | Reactive or proactive | Reactive | Proactive | | Written by | Anyone who finds a bug | QA engineer, developer | | Lifecycle | Created, fixed, closed | Created, maintained, reused | | Outcome | Bug gets fixed | Pass or fail result |

When to Write a Bug Report

Write a bug report when:

You find something that doesn't work as intended
An error message appears that shouldn't
A feature behaves differently than specified
The application crashes or becomes unresponsive
Data is displayed incorrectly
A security vulnerability is discovered

The goal of a bug report is to give developers enough information to reproduce and fix the issue. A good bug report eliminates the need for back-and-forth questions.

When to Write a Test Case

Write a test case when:

You're about to test a new feature for the first time
You want to document "this is what correct looks like"
You need a reusable script for regression testing
You're onboarding new QA team members
You're building a test library for automated testing

Test cases are especially valuable for regression testing — running the same tests repeatedly to ensure old features still work after new changes.

Can the Same Recording Generate Both?

Yes — and this is one of the most powerful capabilities of modern AI testing tools.

Test Buggy records your browser session and can generate either a bug report or a test case from the same recording:

Bug Report mode: AI analyzes your session, identifies the point of failure, and generates a structured bug report with steps, expected/actual results, severity, and evidence.

Test Case mode: AI analyzes your session, identifies the feature being exercised, and generates a structured test case with preconditions, numbered steps, expected results, and priority.

Same recording. Different output. Depending on what you need.

A Practical Example

You're testing a login feature. You enter valid credentials and the page returns a 500 error.

As a bug report:

Summary: Login returns HTTP 500 with valid credentials
Steps:
1. Navigate to /login
2. Enter valid email and password
3. Click "Sign In"
Expected: Redirect to /dashboard
Actual: Page shows "Something went wrong" — 
        Console: POST /api/auth/login 500
Severity: High

As a test case for the same flow (before the bug existed):

Title: Verify successful login with valid credentials
Preconditions: User account exists and is active
Steps:
1. Navigate to /login
2. Enter registered email address
3. Enter correct password
4. Click "Sign In"
Expected Result: User is redirected to /dashboard
                 Welcome message displays user's name
Priority: High

Same feature. Same steps. Different document, different purpose.

Which Do You Need More Of?

For most small teams and startups: more bug reports, better documented.

The majority of QA pain comes from poorly documented bugs that bounce back and forth between developers and testers. Fixing the documentation quality of bug reports has a bigger immediate impact than building a comprehensive test case library.

Once your bug documentation is solid, invest in test cases for your core user journeys — login, signup, payment, the critical paths that can't break.

Automate Both with AI

The reason most teams have weak bug reports and sparse test case libraries is simple: writing them is time-consuming and tedious.

AI removes that friction. Test Buggy generates professional bug reports and test cases from browser recordings in about 3 seconds. Both formats. Both correct. Ready to export to Jira, CSV, PDF, or paste directly into your AI coding assistant.

10 free credits to start — install from the Chrome Web Store.

Test Cases vs. Bug Reports: What's the Difference and When to Use Each