WEBDEV-7261 Fix discrepancy affecting old year-only publish dates (#418)

* Fix discrepancy affecting old year-only publish dates

* Fix expected types to strings not numbers

Author: latonv

src/utils/format-date.ts

@@ -20,8 +20,10 @@ export function formatDate(
 
   switch (format) {
     case 'year-only':
-      options.year = 'numeric';
-      break;
+      // If we're only using the year, ensure we output the correct UTC year and not
+      // the local year. If the local timezone is used, we can get strange off-by-one
+      // errors due to quirks of timezone handling for older years.
+      return `${date.getUTCFullYear()}`;
     case 'short':
       options.month = 'short';
       options.year = 'numeric';

test/utils/format-date.test.ts

@@ -16,6 +16,23 @@ describe('formatDate', () => {
     expect(formatDate(testDate, 'long')).to.equal('Dec 09, 2020');
   });
 
+  it('returns year-only date when year-only DateFormat', () => {
+    expect(formatDate(testDate, 'year-only')).to.equal('2020');
+  });
+
+  it('returns correct year for old "Jan 1 at midnight" dates and year-only DateFormat', () => {
+    // Many standard timezones have a discontinuity in date parsing at some point during
+    // the 19th or 20th century, corresponding to the creation of the timezone.
+    // Dates prior to the discontinuity generally have a non-hour-aligned timezone offset
+    // which can throw off the calculated year for dates which are close to a year boundary.
+    // This is particularly problematic for "Jan 1 at midnight" dates, which are what we
+    // receive from the search engine for date metadata that only specifies the year.
+    // So we must ensure these older dates still output the correct year, not the prior one.
+    expect(formatDate(new Date('1234-01-01T00:00:00Z'), 'year-only')).to.equal(
+      '1234'
+    );
+  });
+
   it('returns locale formatted date', () => {
     expect(formatDate(testDate, 'long', 'de-DE')).to.equal('09. Dez. 2020');
   });