Engineering

Test Case Generator

Generate edge-case-focused test scenarios for any function, feature, or API endpoint — covering boundary values, failure modes, and regression risks.

Open in System Prompt Generator

Overview

Writing complete tests requires thinking beyond the happy path: boundary values, empty inputs, concurrency issues, permission edge cases. Set this up once and use it to systematically enumerate test scenarios for any function or feature — producing structured test ideas your team can implement in their preferred testing framework.

How to use this resource

Describe the target

Paste the function signature, feature spec, or API endpoint description.
Specify the framework

Optionally mention your testing framework (xUnit, Jest, pytest) so scenario names match conventions.
Run through the assistant

Send the description with this system prompt to your AI model.
Prioritize and implement

Review the generated scenarios, prioritize by risk, and implement the most critical ones first.

Why This Works

Categorizing test cases by type (boundary, permission, concurrency) ensures systematic coverage rather than ad-hoc enumeration
Requesting scenarios not code keeps the output implementation-agnostic — works for any framework or language
Regression risk section forces the AI to reason about future failure modes, not just current behavior
Flagging cases that require mocking surfaces test infrastructure decisions before implementation begins

Best for

Functions with non-trivial input validation logic
Public API endpoints with permission requirements
Modules at risk of regression after a major refactor
Features where edge-case failures have high user impact

Not for

Generating runnable test code — this produces scenarios, not implementations
Performance or load testing — use a dedicated benchmarking tool instead
UI pixel-perfect or visual regression testing

Use cases

Generating test plans for a new API endpoint before implementation
Expanding unit test coverage for an undertested module
Creating Playwright or Selenium scenario ideas for E2E test suites
Reviewing a feature spec for testability before writing a single line of code

FAQ

Does the test case generator write runnable test code or just scenarios?

Scenarios only. The system prompt ends with "Do not write the test code — produce test scenarios that the engineer will implement," and each case gives a descriptive name, input/preconditions, and expected outcome. Keeping it implementation-agnostic means the output works for xUnit, Jest, or pytest — but you write the actual tests and run them.

What test categories does this system prompt force the AI to cover?

Six, so coverage is systematic rather than ad-hoc: Happy Path, Boundary Values, Error & Failure Cases, Permission & Authorization, Concurrency & State, and Regression Risks. The Regression Risks section specifically asks for edge cases likely to break in future refactors, and the prompt tells the model to flag any case that requires mocking or test doubles.

Customize This Resource

Opens this resource in System Prompt Generator with the fields pre-filled. Customize role, tone, and behavior rules — then generate your prompt.

Open in System Prompt Generator

Prompt Template

Copy it as-is, or use Open in System Prompt Generator to load it pre-filled and customize it with your own context.

You are a senior QA engineer and test architect.

When given a function signature, feature description, or API endpoint, generate a comprehensive set of test cases. Organize them under the following categories:

## Happy Path
The standard, expected behavior under normal conditions.

## Boundary Values
Minimum, maximum, and just-outside-range inputs. Include empty strings, zero values, and null where applicable.

## Error & Failure Cases
Invalid inputs, missing required fields, malformed data, and expected exceptions.

## Permission & Authorization
Access by unauthorized users, expired tokens, and insufficient permissions.

## Concurrency & State
Race conditions, double-submissions, partial state, and concurrent modifications where relevant.

## Regression Risks
Edge cases that are likely to break in future refactors based on the current implementation.

For each test case provide:
- A descriptive test name
- Input / preconditions
- Expected outcome

Do not write the test code — produce test scenarios that the engineer will implement. Flag any cases that require mocking or test doubles.

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