Fix the timezone test and a missing minus in the timezone fallback (#986

)

src/sources/timezone.test.ts

@@ -1,18 +1,65 @@
+import { withMockProperties } from '../../tests/utils'
 import getTimezone from './timezone'
 
 describe('Sources', () => {
   describe('timezone', () => {
     it('returns a tz identifier in all supported browsers', () => {
       const result = getTimezone()
 
-      // Some devices on BrowserStack return 'UTC'.
-      if (result === 'UTC') {
+      // Some devices on BrowserStack return 'UTC', some '+00:00'.
+      if (result === 'UTC' || /^[+-]\d{2}:\d{2}$/.test(String(result))) {
         return
       }
 
       // We expect all modern browsers (with default settings) to return a TZ identifier,
       // like 'Europe/Berlin' or 'America/Argentina/Buenos_Aires'.
       expect(result).toMatch(/^([a-z]\/+)?[a-z]+\/[a-z_]+$/gi)
     })
+
+    describe('fallbacks', () => {
+      function withNoTimezone(januaryOffset: number, julyOffset: number, action: () => void) {
+        class MockDate {
+          args: unknown[]
+
+          constructor(...args: unknown[]) {
+            this.args = args
+          }
+
+          getFullYear() {
+            return 2024
+          }
+
+          getTimezoneOffset() {
+            if (this.args[1] === 0) {
+              return januaryOffset
+            }
+            if (this.args[1] === 6) {
+              return julyOffset
+            }
+            throw TypeError('Unexpected constructor arguments')
+          }
+        }
+
+        return withMockProperties(window, { Date: { value: MockDate }, Intl: undefined }, action)
+      }
+
+      it('in the northern eastern hemisphere (Berlin)', async () => {
+        await withNoTimezone(1 * -60, 2 * -60, () => {
+          expect(getTimezone()).toEqual('UTC+60')
+        })
+      })
+
+      it('in the southern western hemisphere (Santiago)', async () => {
+        await withNoTimezone(-3 * -60, -4 * -60, () => {
+          expect(getTimezone()).toEqual('UTC-240')
+        })
+      })
+
+      it('in the middle', async () => {
+        await withNoTimezone(0, 0, () => {
+          expect(getTimezone()).toEqual('UTC+0')
+        })
+      })
+    })
   })
 })

src/sources/timezone.ts

@@ -12,7 +12,7 @@ export default function getTimezone(): string {
   // For browsers that don't support timezone names
   // The minus is intentional because the JS offset is opposite to the real offset
   const offset = -getTimezoneOffset()
-  return `UTC${offset >= 0 ? '+' : ''}${Math.abs(offset)}`
+  return `UTC${offset >= 0 ? '+' : ''}${offset}`
 }
 
 function getTimezoneOffset(): number {