fix(other): validate current two-digit year when it matches century prefix

[stevechen256-source]

Summary of changes

Fixes #127 — a card expiration such as 07/20 was reported as invalid for the entire year 2020.

What & Why

In expirationYear, the two-digit-year branch first checked whether the input matched the century prefix of the current year (String(currentYear).substr(0, 2)):

if (String(currentYear).substr(0, 2) === value) {
  return verification(false, true); // potentially valid only
}

During 2020 the century prefix is "20", which is also a complete two-digit year. So "20" was always short-circuited to "potentially valid" and never evaluated as the current year. Every MM/YY expiration with YY = 20 therefore failed validation in 2020 (e.g. expirationDate("07/20") on 2020-01-01 → { isValid: false }), even though July 2020 was in the future. The same bug mis-classified future years whose two-digit form matched the century prefix (e.g. "20" entered in 2018/2019).

Changes

• src/expiration-year.ts: compute the actual validity (isCurrentYear / valid window) before the century-prefix check, so a complete two-digit year that is the current year or within the valid window is accepted. The century-prefix match now only serves as a "potentially valid" fallback for partially typed 4-digit years (e.g. "20" → "2021").
• src/__tests__/expiration-year.ts: regression tests with the system clock set to 2020-01-01.
• src/__tests__/expiration-date.ts: regression tests asserting 07/20 is valid (and 06/19 is invalid) in 2020.

Test plan

npm test (jest + eslint):

Test Suites: 11 passed, 11 total
Tests:       588 passed, 588 total

Before the fix, the new regression cases failed:

expirationYear('20') in 2020: {"isValid":false,"isPotentiallyValid":true,"isCurrentYear":false}  // expected isValid: true
expirationDate('07/20') in 2020: {"isValid":false,...}                                           // expected isValid: true

After the fix both return isValid: true. Full suite passes with coverage thresholds met.

Checklist

• Added a changelog entry
• Relevant test coverage
• Tested and confirmed flows affected by this change are functioning as expected

Authors

stevechen256-source

[github-actions]

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