Testing and Debugging the Guard Proving the trust boundary instead of assuming it works
Course principle: a user ID becomes trusted only after the access token has been cryptographically verified by the backend.
Manual test matrix Test Expected
PowerShell example $api = 'http://127.0.0.1:4000' $token = '<paste-current-development-access-token>'
Invoke-RestMethod ` -Uri "$api/auth/me" ` -Headers @{ Authorization = "Bearer $token" }
Do not commit access tokens into test scripts. For a durable automated suite, acquire test credentials through a dedicated test setup or inject short-lived test tokens securely.
Debug by layer Authentication debugging order
Does Next.js have a current session?
Was Authorization header sent?
Did CORS allow browser request?
Did guard extract Bearer token?
Did getClaims verify it?
Was request.user attached?
Never log • Raw Authorization header
• Access token
• Refresh token
• Session cookie
• Supabase secret/service role key
Safe to log requestId, route, HTTP method, authentication failure category, verified user ID when appropriate for audit policy, and timing - without credential material. Source note: verified against current Supabase Auth/getClaims/signing-key guidance and NestJS authentication/authorization docs. Full URLs and version notes are included in SOURCE_NOTES.txt.
Tests are executable behavioral contracts. Good tests protect meaningful invariants and failure cases, not implementation trivia.
Restate the goal of “Testing Debugging and Observability” as one observable behavior. Write the success signal before touching code.
Trace the boundary map: behavior contract → arrange → act → assert → regression signal. Mark the one boundary this lesson changes.
Inspect the current repository state and record the exact files, route, table, or runtime involved. Avoid creating an abstraction before you can name the existing owner.
Implement the smallest vertical slice. Add one coherent change, run the narrowest verification command, and read the output before continuing.
Connect the slice to TaskFlow’s phase artifact: Authentication guard + verification service + current-user helper + protected /auth/me and task routes.. Verify behavior from the outside as a user or API client would.
Create one controlled failure that is safe to reproduce. Predict the symptom first, capture evidence, locate the earliest broken boundary, then fix only that cause.
Close the reference and rebuild or explain the core change from memory. Record what you would monitor or test before trusting the same change in production.
it("rejects deleting another member's task", async () => {
const response = await asUser(bob).delete(`/tasks/${aliceTask.id}`);
expect(response.status).toBe(403);
expect(await taskStillExists(aliceTask.id)).toBe(true);
});Do not copy this as a finished answer. Predict what each boundary does, type the smallest useful slice, run it, then compare the result with your prediction.
Look for shared database state, timers, globals, unordered execution, or missing cleanup before adding retries.
Move the highest-risk boundary to an integration test with the real adapter/database.
Without copying the final source, create a second small scenario that applies “Testing Debugging and Observability” to a different TaskFlow resource or input. Write the acceptance criteria first, implement it, and provide the evidence that each criterion is satisfied.
Normalize verified claims into an application user identity object.
Use the smallest change that demonstrates this lesson. Stop after it works and capture evidence.Decoding JWT without signature verification
Predict the symptom before causing the failure. Then locate the earliest boundary where reality diverges from expectation.Why does this responsibility live here, what input does it trust, what output proves success, and what would go wrong if another layer owned it?
If your explanation is vague, repeat the boundary trace before moving on.Close the reference. Reproduce the core idea from memory or explain the exact request/data flow aloud. Then check your diff or notes for accidental shortcuts that bypass validation, authorization, error handling, or verification earned in earlier phases.