Test Suite Generator from Source Code

The Prompt

You are a senior {{language}} test engineer. Generate a practical, high-signal test suite for the code below.

Test framework:
{{test_framework}}

Code under test:
{{code_under_test}}

Critical behavior that must not break:
{{critical_paths}}

Return output in this exact structure:
1) Risk-based test plan (what matters most and why)
2) Prioritized test cases table (P0/P1/P2 with short rationale)
3) Edge cases and failure-mode tests
4) Table-driven or parameterized test matrix where applicable
5) Runnable starter test file in {{test_framework}}
6) Gaps and assumptions (what cannot be tested from current context)

Constraints:
- Focus first on behavior correctness, then edge cases, then implementation details.
- Avoid brittle tests coupled to private internals.
- Prefer deterministic tests; mock external systems explicitly.
- Include at least one negative test per critical path.

When to Use

Use this when you have working code but weak test coverage, or when you want a fast first draft of meaningful tests. It works well for functions, modules, service handlers, and data transforms.

Best use cases:

• New feature shipped without enough tests
• Legacy code where test debt has accumulated
• Refactors where you need confidence before changes
• Bugs that should be locked down with regression tests

This prompt is designed for practical output, not academic completeness. You get a prioritized list and runnable starter tests you can paste directly into your codebase and iterate.

Variables

Variable	Description	Good input examples
language	Programming language of the code	TypeScript, Python, Java
test_framework	Framework and style requirements	Vitest, Jest, Pytest, JUnit 5
code_under_test	Actual source code or key excerpt	Class, function, endpoint handler
critical_paths	Business-critical behaviors to protect	”payment success path”, “retry backoff logic”

Tips & Variations

• Ask for “minimum high-value suite under 30 minutes” when you need speed.
• Add “include fixture factory helpers” for repeated test setup.
• Add CI constraints like “tests must run under 2 minutes.”
• For API code, request explicit status code and error body assertions.
• After generating tests, run a second prompt: “Suggest missing cases based on mutation testing mindset.”

If output is too broad, narrow scope to one module and one critical path per run. Iterative prompts usually produce better tests than one giant request.

Example Output

P0: Returns 401 when auth token is missing.

P1: Retries network timeout exactly 3 times with exponential backoff.

Starter test snippet (Vitest):

it("returns 401 when token is missing", async () => {
  const res = await handler(mockReqWithoutToken);
  expect(res.status).toBe(401);
});