Add unit tests to bindReporter

[nucliweb]

In this Pull Request

Add unit tests to bindReporter

The let fixDelta = reporters[1].delta.toFixed(2) avoids floating point precision issues in the test assertion by rounding the delta value to 2 decimal places before comparing it.

Test error

✖ should calculate delta correctly between reports (1.825833ms)
  AssertionError [ERR_ASSERTION]: 0.04999999999999999 == 0.05
      at TestContext.<anonymous> (file:///.../web-vitals/test/unit/bindReporter-test.js:104:14)
      at Test.runInAsyncScope (node:async_hooks:203:9)
      at Test.run (node:internal/test_runner/test:631:25)
      at Test.start (node:internal/test_runner/test:542:17)
      at node:internal/test_runner/test:946:71
      at node:internal/per_context/primordials:487:82
      at new Promise (<anonymous>)
      at new SafePromise (node:internal/per_context/primordials:455:29)
      at node:internal/per_context/primordials:487:9
      at Array.map (<anonymous>) {
    generatedMessage: true,
    code: 'ERR_ASSERTION',
    actual: 0.04999999999999999,
    expected: 0.05,
    operator: '=='
  }

[tunetheweb]

Love having more tests!!!

However, not loving the toFixed(2) change. Especially as this'll narrow LCP to 0.1 second precision?

The metric.delta = Number(delta.toFixed(2))) change avoids floating point precision issues in the test assertion by rounding the delta value to 2 decimal places before comparing it.

Why can't we do this rounding in the test?

[nucliweb]

Yes, I'll move to the test 👍

[nucliweb]

@tunetheweb done,