Fix pluralization when maxDecimalPoints truncates the count to 1

[dualfroz]

Problem

When the maxDecimalPoints option truncates a unit count down to exactly 1,
the rendered number and the unit word disagree. The number is shown as 1 but
the word is pluralized:

const humanizeDuration = require("humanize-duration");

humanizeDuration(1500, { maxDecimalPoints: 0 }); // "1 seconds"  (expected "1 second")
humanizeDuration(1005, { maxDecimalPoints: 2 }); // "1 seconds"  (expected "1 second")

The bug is language-independent; any language whose unit word is a function of
the count is affected (for example German returns "1 Sekunden" instead of
"1 Sekunde").

Root cause

humanize-duration.js, in renderPiece.

The displayed count is normalizedUnitCount, computed from maxDecimalPoints:

var normalizedUnitCount =
  maxDecimalPoints === void 0
    ? unitCount
    : Math.floor(unitCount * Math.pow(10, maxDecimalPoints)) /
      Math.pow(10, maxDecimalPoints);
var countStr = normalizedUnitCount.toString();

but the unit word was pluralized from the raw, un-truncated unitCount:

if (typeof languageWord === "function") {
  word = languageWord(unitCount);
}

So 1.5 seconds with maxDecimalPoints: 0 renders the count as "1" (from
normalizedUnitCount) while languageWord(1.5) returns the plural form, giving
"1 seconds".

Fix

Pluralize based on the count that is actually rendered, normalizedUnitCount:

if (typeof languageWord === "function") {
  word = languageWord(normalizedUnitCount);
}

When maxDecimalPoints is unset, normalizedUnitCount === unitCount, so
existing behavior is unchanged. The fix only affects cases where the option
truncates the count.

Test

Added a test to test/humanizer.js covering the truncated-to-one case, a
truncated count that stays plural, and the same mechanism in German:

assert.strictEqual(humanizer({ maxDecimalPoints: 0 })(1500), "1 second");
assert.strictEqual(humanizer({ maxDecimalPoints: 2 })(1005), "1 second");
assert.strictEqual(humanizer({ maxDecimalPoints: 0 })(2500), "2 seconds");
assert.strictEqual(
  humanizer({ language: "de", maxDecimalPoints: 0 })(1500),
  "1 Sekunde"
);

Counterfactual (revert the one-line fix in renderPiece):

Expected values to be strictly equal:
expected: '1 second'
actual:   '1 seconds'

[EvanHahn]

Thanks. I'll review in the next few weeks.

[EvanHahn]

I made some changes to this and merged it in 924c2a1. This has been released in humanize-duration@3.35.0.

Thank you!