test: add unit tests for tier helpers

[Ayushmann13479]

🎯 Description

Adds a new unit test file for src/tiers.js to improve coverage of subscription tier helper functions and environment-variable override behavior.

🤔 Why?

Issue #114 requested unit tests for the pure functions in src/tiers.js. These functions are a good target for testing because they have no database or network dependencies and contain important tier policy logic.

📝 Changes

• Added tests/unit/tiers.test.js
• Added tests for isValidTier()
• Added tests for TIER_NAMES and DEFAULT_TIER
• Added tests for getTierDefinitions()
• Added tests for environment variable overrides
• Added tests for "unlimited" value handling
• Added tests for invalid/empty environment values
• Added tests for getTierPolicy() fallback behavior

🧪 How to Test?

1. Install dependencies:

   npm install

[surpradhan]

Thanks for taking this on, @Ayushmann13479! Solid first contribution. The framework and style match the project well, and the acceptance criteria from issue #114 are covered. Two things to address:

Must fix

parseLimit("0") boundary is untested. The guard in parseLimit is n < 0, so TIER_FREE_EVENT_QUOTA=0 returns 0, not the built-in default. This means an operator who sets the env var to "0" accidentally hard-blocks all event ingest for the free tier. Please add a test that documents this behaviour:

test("zero is returned as-is (not treated as fallback)", () => {
  process.env.TIER_FREE_EVENT_QUOTA = "0";
  assert.equal(getTierDefinitions().free.event_quota, 0);
});

Nits (optional but appreciated)

• Missing trailing newline at end of file. ESLint won't catch it in this project, but editors and git diff flag it. Just add a newline after the last });.
• isValidTier(null) and isValidTier(undefined) both safely return false but are untested. A quick two-liner in the existing isValidTier describe block would close that gap.

[Ayushmann13479]

Thanks for the review
I've addressed the requested changes:

• Added coverage for TIER_FREE_EVENT_QUOTA="0" to verify that zero is returned as-is and not treated as a fallback.
• Added tests for isValidTier(null) and isValidTier(undefined).
• Added the missing trailing newline at the end of the file.

Please take another look.

[surpradhan]

Thanks for tackling this -- the structure is solid and all the edge cases from the issue are covered. Two things to address before we merge:

1. Indentation in the "zero is returned as-is" test (lines ~85-90)
The body of that test block is 2-space indented while the rest of the file uses 4-space. There is also a trailing space after the closing });. Quick fix -- just re-indent to match the surrounding tests.

2. process.env replacement pattern
Replacing the whole process.env object works, but is fragile (snapshot is taken at module-load time, not test-run time). The project convention is to mutate specific keys and delete them in afterEach. Something like:

const TIER_KEYS = [
  "TIER_FREE_EVENT_QUOTA",       "TIER_FREE_RETENTION_DAYS",
  "TIER_TEAM_EVENT_QUOTA",       "TIER_TEAM_RETENTION_DAYS",
  "TIER_ENTERPRISE_EVENT_QUOTA", "TIER_ENTERPRISE_RETENTION_DAYS",
];
afterEach(() => { for (const k of TIER_KEYS) delete process.env[k]; });

Then each test just sets the vars it needs directly -- no beforeEach needed at all.

Optional but nice-to-have: add isValidTier("") to the "returns false" test -- empty string is a realistic bad input from a malformed project row.

[Ayushmann13479]

Thanks for the review! I've addressed the requested changes:

1. Removed the beforeEach pattern and switched to cleaning only the tier-related environment variables in afterEach.
2. Fixed the indentation and trailing whitespace in the zero-value test.
3. Added the isValidTier("") test.

Please let me know if there's anything else you'd like me to adjust.

[surpradhan]

Good fixes -- the process.env replacement is gone and isValidTier("") is in. All the functional feedback is addressed.

One remaining nit: the closing }); on the "zero is returned as-is" test is still at column 0 instead of column 2. Also TIER_KEYS and afterEach use 4-space indentation while the describe/test blocks use 2-space -- worth making consistent. Both are cosmetic only.

Happy to merge once those are tidied up.

[Ayushmann13479]

Thanks! I've cleaned up the indentation to match the rest of the file.

[surpradhan]

Thank you for this contribution, @Ayushmann13479! The tier helper unit tests are a great addition to the test suite — clean coverage of isValidTier(), getTierDefinitions(), env-var overrides, and getTierPolicy() fallback behavior. This closes issue #114.