Review a trial access policy

Review exercise · TypeScript

Review brief

Beginner20 min

A subscription service is consolidating scattered access checks into one policy function. The decision gates product access for every request, so review its precedence, exact time behavior, fail-safe handling, and test protection before rollout.

Behavioral contract

The supplied now value is the authoritative clock for the decision; the function must not read the system clock.
Suspension has highest precedence: every suspended account is denied with reason suspended, regardless of plan or trial data.
The only recognized plans are trial, pro, and business. A non-suspended pro or business account is allowed with reason paid-plan.
A non-suspended trial is allowed with reason active-trial only when trialEndsAt exists and is strictly later than now. Equality is expired; a missing or past expiry is denied with reason trial-expired.
A missing, null, or unknown plan is denied with reason invalid-plan unless suspension already determines the result.

Review instructions

1Review only the changed code against the behavioral contract in the brief.
2Anchor each finding to the narrowest useful changed line and explain the access impact.
3Recommend a direction rather than writing replacement code.
4Prioritize no more than four findings.

Learning objectives

• Review precedence among business rules
• Test exact time boundaries
• Choose fail-safe behavior for unknown policy inputs

src/trial-access-policy.tsTypeScript

@@ -0,0 +1,40 @@

1+export interface AccountAccessState {

2+ plan?: string | null;

3+ suspended: boolean;

4+ trialEndsAt: Date | null;

5+}

7+export type AccessReason =

8+ | "paid-plan"

9+ | "active-trial"

10+ | "suspended"

11+ | "trial-expired"

12+ | "invalid-plan";

13+

14+export interface AccessDecision {

15+ allowed: boolean;

16+ reason: AccessReason;

17+}

18+

19+export function decideAccountAccess(

20+ account: AccountAccessState,

21+ now: Date,

22+): AccessDecision {

23+ if (account.plan === "pro" || account.plan === "business") {

24+ return { allowed: true, reason: "paid-plan" };

25+ }

26+

27+ if (account.suspended) {

28+ return { allowed: false, reason: "suspended" };

29+ }

30+

31+ if (account.plan === "trial") {

32+ if (account.trialEndsAt && account.trialEndsAt >= now) {

33+ return { allowed: true, reason: "active-trial" };

34+ }

35+

36+ return { allowed: false, reason: "trial-expired" };

37+ }

38+

39+ return { allowed: true, reason: "paid-plan" };

40+}

Reference solution

The findings below are ordered by priority.

Findings

1. Paid plans bypass the suspension rule

Location: src/trial-access-policy.ts:23-29

The function grants pro and business accounts before checking suspended. A suspended paid account therefore retains access even though suspension is the highest-precedence rule for every plan.

Evaluate suspension first and return the suspended denial before any plan can grant access.

2. Missing and unknown plan values grant paid access

Location: src/trial-access-policy.ts:31-39

Any plan value that is not trial, pro, or business reaches the final successful paid-plan result. That includes null, an omitted plan, and new or misspelled strings, turning incomplete policy data into an access grant.

Handle each recognized plan explicitly and return the documented invalid-plan denial for every other value.

3. A trial remains active at its exclusive expiry instant

Location: src/trial-access-policy.ts:31-36

The >= comparison allows access when trialEndsAt equals the supplied authoritative now. The contract defines the expiry as exclusive, so access must already be denied at that instant.

Require trialEndsAt to be strictly later than now; continue denying a trial with no expiry.

4. The tests omit the precedence, boundary, and fail-safe cases

Location: src/trial-access-policy.test.ts:8-31

The tests cover only an ordinary future trial and an expiry strictly in the past. They do not exercise a suspended paid account, expiry exactly at now, or missing and unknown plans, so all three policy regressions pass the suite.

Add decision-table cases for suspension across plan types, the exact expiry instant, and every invalid-plan representation while asserting both allowed and reason.

Reasonable non-findings

Receiving now as an argument provides the authoritative, deterministic clock required by the contract.
A recognized paid account does not need a trial expiry date when it is not suspended.
Denying a trial whose expiry is before now or missing is correct.
Returning a reason together with the boolean decision is useful and matches the stated policy result.