Add Temporal half-rounding boundary tests across all units

test/built-ins/Temporal/PlainDate/prototype/since/roundingmode-half-boundary.js

@@ -0,0 +1,127 @@
+// Copyright (C) 2026 Rudolph Gottesheim. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plaindate.prototype.since
+description: Half rounding modes at the exact 0.5 boundary for years and months
+info: |
+  Tests that all rounding modes correctly break ties at the exact 0.5 boundary
+  in RoundRelativeDuration in the negative direction, for both odd and even
+  integer parts (distinguishing halfEven from other modes). In the negative
+  direction, halfExpand and halfCeil diverge (away from zero vs toward positive
+  infinity).
+
+  Years: dates 2019-01-01 / 2020-07-02 produce a difference of -1 year minus
+  183 days. The year 2020 is a leap year (366 days), so fractional progress =
+  183/366 = 0.5. Dates 2018-01-01 / 2020-07-02 produce -2 years minus 183 days
+  (even integer part).
+
+  Months: dates 2019-01-01 / 2019-02-15 produce -1 month minus 14 days.
+  February 2019 has 28 days, so fractional progress = 14/28 = 0.5.
+  Dates 2018-12-01 / 2019-02-15 produce -2 months minus 14 days (even integer
+  part).
+includes: [temporalHelpers.js]
+features: [Temporal]
+---*/
+
+// --- years ---
+
+// -1.5 years: odd integer part (1) + exact 0.5 fractional progress
+const yearEarlier1 = new Temporal.PlainDate(2019, 1, 1);
+const yearLater = new Temporal.PlainDate(2020, 7, 2);
+
+assert.sameValue(
+  yearEarlier1.until(yearLater).total({ unit: "years", relativeTo: yearEarlier1 }),
+  1.5,
+  "1.5-year duration is on a 0.5 boundary"
+);
+
+for (const mode of ["trunc", "ceil", "halfTrunc", "halfCeil"]) {
+  TemporalHelpers.assertDuration(
+    yearEarlier1.since(yearLater, { smallestUnit: "years", roundingMode: mode }),
+    -1, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+    `-1.5 years with ${mode} rounds toward zero`
+  );
+}
+for (const mode of ["floor", "expand", "halfExpand", "halfFloor", "halfEven"]) {
+  TemporalHelpers.assertDuration(
+    yearEarlier1.since(yearLater, { smallestUnit: "years", roundingMode: mode }),
+    -2, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+    `-1.5 years with ${mode} rounds away from zero`
+  );
+}
+
+// -2.5 years: even integer part (2) — distinguishes halfEven from halfExpand
+const yearEarlier2 = new Temporal.PlainDate(2018, 1, 1);
+
+assert.sameValue(
+  yearEarlier2.until(yearLater).total({ unit: "years", relativeTo: yearEarlier2 }),
+  2.5,
+  "2.5-year duration is on a 0.5 boundary"
+);
+
+for (const mode of ["trunc", "ceil", "halfTrunc", "halfCeil", "halfEven"]) {
+  TemporalHelpers.assertDuration(
+    yearEarlier2.since(yearLater, { smallestUnit: "years", roundingMode: mode }),
+    -2, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+    `-2.5 years with ${mode} rounds toward zero`
+  );
+}
+for (const mode of ["floor", "expand", "halfExpand", "halfFloor"]) {
+  TemporalHelpers.assertDuration(
+    yearEarlier2.since(yearLater, { smallestUnit: "years", roundingMode: mode }),
+    -3, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+    `-2.5 years with ${mode} rounds away from zero`
+  );
+}
+
+// --- months ---
+
+// -1.5 months: odd integer part (1) + exact 0.5 fractional progress
+const monthEarlier1 = new Temporal.PlainDate(2019, 1, 1);
+const monthLater = new Temporal.PlainDate(2019, 2, 15);
+
+assert.sameValue(
+  monthEarlier1.until(monthLater).total({ unit: "months", relativeTo: monthEarlier1 }),
+  1.5,
+  "1.5-month duration is on a 0.5 boundary"
+);
+
+for (const mode of ["trunc", "ceil", "halfTrunc", "halfCeil"]) {
+  TemporalHelpers.assertDuration(
+    monthEarlier1.since(monthLater, { smallestUnit: "months", roundingMode: mode }),
+    0, -1, 0, 0, 0, 0, 0, 0, 0, 0,
+    `-1.5 months with ${mode} rounds toward zero`
+  );
+}
+for (const mode of ["floor", "expand", "halfExpand", "halfFloor", "halfEven"]) {
+  TemporalHelpers.assertDuration(
+    monthEarlier1.since(monthLater, { smallestUnit: "months", roundingMode: mode }),
+    0, -2, 0, 0, 0, 0, 0, 0, 0, 0,
+    `-1.5 months with ${mode} rounds away from zero`
+  );
+}
+
+// -2.5 months: even integer part (2) — distinguishes halfEven from halfExpand
+const monthEarlier2 = new Temporal.PlainDate(2018, 12, 1);
+
+assert.sameValue(
+  monthEarlier2.until(monthLater).total({ unit: "months", relativeTo: monthEarlier2 }),
+  2.5,
+  "2.5-month duration is on a 0.5 boundary"
+);
+
+for (const mode of ["trunc", "ceil", "halfTrunc", "halfCeil", "halfEven"]) {
+  TemporalHelpers.assertDuration(
+    monthEarlier2.since(monthLater, { smallestUnit: "months", roundingMode: mode }),
+    0, -2, 0, 0, 0, 0, 0, 0, 0, 0,
+    `-2.5 months with ${mode} rounds toward zero`
+  );
+}
+for (const mode of ["floor", "expand", "halfExpand", "halfFloor"]) {
+  TemporalHelpers.assertDuration(
+    monthEarlier2.since(monthLater, { smallestUnit: "months", roundingMode: mode }),
+    0, -3, 0, 0, 0, 0, 0, 0, 0, 0,
+    `-2.5 months with ${mode} rounds away from zero`
+  );
+}

test/built-ins/Temporal/PlainDate/prototype/until/roundingmode-half-boundary.js

@@ -0,0 +1,123 @@
+// Copyright (C) 2026 Rudolph Gottesheim. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plaindate.prototype.until
+description: Half rounding modes at the exact 0.5 boundary for years and months
+info: |
+  Tests that all rounding modes correctly break ties at the exact 0.5 boundary
+  in RoundRelativeDuration, for both odd and even integer parts (distinguishing
+  halfEven from other modes).
+
+  Years: dates 2019-01-01 / 2020-07-02 produce 1 year + 183 days. The year
+  2020 is a leap year (366 days), so fractional progress = 183/366 = 0.5.
+  Dates 2018-01-01 / 2020-07-02 produce 2 years + 183 days (even integer part).
+
+  Months: dates 2019-01-01 / 2019-02-15 produce 1 month + 14 days. February
+  2019 has 28 days, so fractional progress = 14/28 = 0.5. Dates 2018-12-01 /
+  2019-02-15 produce 2 months + 14 days (even integer part).
+includes: [temporalHelpers.js]
+features: [Temporal]
+---*/
+
+// --- years ---
+
+// 1.5 years: odd integer part (1) + exact 0.5 fractional progress
+const yearEarlier1 = new Temporal.PlainDate(2019, 1, 1);
+const yearLater = new Temporal.PlainDate(2020, 7, 2);
+
+assert.sameValue(
+  yearEarlier1.until(yearLater).total({ unit: "years", relativeTo: yearEarlier1 }),
+  1.5,
+  "1.5-year duration is on a 0.5 boundary"
+);
+
+for (const mode of ["trunc", "floor", "halfTrunc", "halfFloor"]) {
+  TemporalHelpers.assertDuration(
+    yearEarlier1.until(yearLater, { smallestUnit: "years", roundingMode: mode }),
+    1, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+    `1.5 years with ${mode} rounds down to 1`
+  );
+}
+for (const mode of ["ceil", "expand", "halfExpand", "halfCeil", "halfEven"]) {
+  TemporalHelpers.assertDuration(
+    yearEarlier1.until(yearLater, { smallestUnit: "years", roundingMode: mode }),
+    2, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+    `1.5 years with ${mode} rounds up to 2`
+  );
+}
+
+// 2.5 years: even integer part (2) — distinguishes halfEven from halfExpand
+const yearEarlier2 = new Temporal.PlainDate(2018, 1, 1);
+
+assert.sameValue(
+  yearEarlier2.until(yearLater).total({ unit: "years", relativeTo: yearEarlier2 }),
+  2.5,
+  "2.5-year duration is on a 0.5 boundary"
+);
+
+for (const mode of ["trunc", "floor", "halfTrunc", "halfFloor", "halfEven"]) {
+  TemporalHelpers.assertDuration(
+    yearEarlier2.until(yearLater, { smallestUnit: "years", roundingMode: mode }),
+    2, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+    `2.5 years with ${mode} rounds down to 2`
+  );
+}
+for (const mode of ["ceil", "expand", "halfExpand", "halfCeil"]) {
+  TemporalHelpers.assertDuration(
+    yearEarlier2.until(yearLater, { smallestUnit: "years", roundingMode: mode }),
+    3, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+    `2.5 years with ${mode} rounds up to 3`
+  );
+}
+
+// --- months ---
+
+// 1.5 months: odd integer part (1) + exact 0.5 fractional progress
+const monthEarlier1 = new Temporal.PlainDate(2019, 1, 1);
+const monthLater = new Temporal.PlainDate(2019, 2, 15);
+
+assert.sameValue(
+  monthEarlier1.until(monthLater).total({ unit: "months", relativeTo: monthEarlier1 }),
+  1.5,
+  "1.5-month duration is on a 0.5 boundary"
+);
+
+for (const mode of ["trunc", "floor", "halfTrunc", "halfFloor"]) {
+  TemporalHelpers.assertDuration(
+    monthEarlier1.until(monthLater, { smallestUnit: "months", roundingMode: mode }),
+    0, 1, 0, 0, 0, 0, 0, 0, 0, 0,
+    `1.5 months with ${mode} rounds down to 1`
+  );
+}
+for (const mode of ["ceil", "expand", "halfExpand", "halfCeil", "halfEven"]) {
+  TemporalHelpers.assertDuration(
+    monthEarlier1.until(monthLater, { smallestUnit: "months", roundingMode: mode }),
+    0, 2, 0, 0, 0, 0, 0, 0, 0, 0,
+    `1.5 months with ${mode} rounds up to 2`
+  );
+}
+
+// 2.5 months: even integer part (2) — distinguishes halfEven from halfExpand
+const monthEarlier2 = new Temporal.PlainDate(2018, 12, 1);
+
+assert.sameValue(
+  monthEarlier2.until(monthLater).total({ unit: "months", relativeTo: monthEarlier2 }),
+  2.5,
+  "2.5-month duration is on a 0.5 boundary"
+);
+
+for (const mode of ["trunc", "floor", "halfTrunc", "halfFloor", "halfEven"]) {
+  TemporalHelpers.assertDuration(
+    monthEarlier2.until(monthLater, { smallestUnit: "months", roundingMode: mode }),
+    0, 2, 0, 0, 0, 0, 0, 0, 0, 0,
+    `2.5 months with ${mode} rounds down to 2`
+  );
+}
+for (const mode of ["ceil", "expand", "halfExpand", "halfCeil"]) {
+  TemporalHelpers.assertDuration(
+    monthEarlier2.until(monthLater, { smallestUnit: "months", roundingMode: mode }),
+    0, 3, 0, 0, 0, 0, 0, 0, 0, 0,
+    `2.5 months with ${mode} rounds up to 3`
+  );
+}