diff --git a/harness/temporalHelpers.js b/harness/temporalHelpers.js
new file mode 100644
index 0000000000..984902aa7b
--- /dev/null
+++ b/harness/temporalHelpers.js
@@ -0,0 +1,82 @@
+// Copyright (C) 2021 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+description: |
+    This defines helper objects and functions for testing Temporal.
+defines: [TemporalHelpers]
+features: [Symbol.species, Symbol.iterator, Temporal]
+---*/
+
+var TemporalHelpers = {
+  /*
+   * Check that any calendar-carrying Temporal object has its [[Calendar]]
+   * internal slot read by ToTemporalCalendar, and does not fetch the calendar
+   * by calling getters.
+   * The custom calendar object is passed in to func() so that it can do its
+   * own additional assertions involving the calendar if necessary. (Sometimes
+   * there is nothing to assert as the calendar isn't stored anywhere that can
+   * be asserted about.)
+   */
+  checkToTemporalCalendarFastPath(func) {
+    class CalendarFastPathCheck extends Temporal.Calendar {
+      constructor() {
+        super("iso8601");
+      }
+
+      toString() {
+        return "fast-path-check";
+      }
+    }
+    const calendar = new CalendarFastPathCheck();
+
+    const plainDate = new Temporal.PlainDate(2000, 5, 2, calendar);
+    const plainDateTime = new Temporal.PlainDateTime(2000, 5, 2, 12, 34, 56, 987, 654, 321, calendar);
+    const plainMonthDay = new Temporal.PlainMonthDay(5, 2, calendar);
+    const plainYearMonth = new Temporal.PlainYearMonth(2000, 5, calendar);
+    const zonedDateTime = new Temporal.ZonedDateTime(1_000_000_000_000_000_000n, "UTC", calendar);
+
+    [plainDate, plainDateTime, plainMonthDay, plainYearMonth, zonedDateTime].forEach((temporalObject) => {
+      const actual = [];
+      const expected = [];
+
+      Object.defineProperty(temporalObject, "calendar", {
+        get() {
+          actual.push("get calendar");
+          return calendar;
+        },
+      });
+
+      func(temporalObject, calendar);
+      assert.compareArray(actual, expected, "calendar getter not called");
+    });
+  },
+
+  /*
+   * specificOffsetTimeZone():
+   *
+   * This returns an instance of a custom time zone class, which returns a
+   * specific custom value from its getOffsetNanosecondsFrom() method. This is
+   * for the purpose of testing the validation of what this method returns.
+   *
+   * It also returns an empty array from getPossibleInstantsFor(), so as to
+   * trigger calls to getOffsetNanosecondsFor() when used from the
+   * BuiltinTimeZoneGetInstantFor operation.
+   */
+  specificOffsetTimeZone(offsetValue) {
+    class SpecificOffsetTimeZone extends Temporal.TimeZone {
+      constructor(offsetValue) {
+        super("UTC");
+        this._offsetValue = offsetValue;
+      }
+
+      getOffsetNanosecondsFor() {
+        return this._offsetValue;
+      }
+
+      getPossibleInstantsFor() {
+        return [];
+      }
+    }
+    return new SpecificOffsetTimeZone(offsetValue);
+  },
+};
diff --git a/test/built-ins/Temporal/now/plainDateTime/calendar-function.js b/test/built-ins/Temporal/now/plainDateTime/calendar-function.js
new file mode 100644
index 0000000000..e780917e8c
--- /dev/null
+++ b/test/built-ins/Temporal/now/plainDateTime/calendar-function.js
@@ -0,0 +1,46 @@
+// Copyright (C) 2020 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.now.plaindatetime
+description: Behavior when provided calendar value is a function
+includes: [compareArray.js]
+features: [Temporal]
+---*/
+
+const actual = [];
+const expected = [
+  "has timeZone.timeZone",
+  "get timeZone.getOffsetNanosecondsFor",
+  "call timeZone.getOffsetNanosecondsFor",
+];
+const calendar = function() {};
+const timeZone = new Proxy({
+  getOffsetNanosecondsFor(instant) {
+    actual.push("call timeZone.getOffsetNanosecondsFor");
+    return -Number(instant.epochNanoseconds % 86400_000_000_000n);
+  },
+}, {
+  has(target, property) {
+    actual.push(`has timeZone.${property}`);
+    return property in target;
+  },
+  get(target, property) {
+    actual.push(`get timeZone.${property}`);
+    return target[property];
+  },
+});
+
+Object.defineProperty(Temporal.Calendar, "from", {
+  get() {
+    actual.push("get Temporal.Calendar.from");
+    return undefined;
+  },
+});
+
+const result = Temporal.now.plainDateTime(calendar, timeZone);
+for (const property of ["hour", "minute", "second", "millisecond", "microsecond", "nanosecond"]) {
+  assert.sameValue(result[property], 0, property);
+}
+
+assert.compareArray(actual, expected);
diff --git a/test/built-ins/Temporal/now/plainDateTime/calendar-object-fail-call-tostring.js b/test/built-ins/Temporal/now/plainDateTime/calendar-object-fail-call-tostring.js
new file mode 100644
index 0000000000..52efb50883
--- /dev/null
+++ b/test/built-ins/Temporal/now/plainDateTime/calendar-object-fail-call-tostring.js
@@ -0,0 +1,20 @@
+// Copyright (C) 2021 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-temporal.now.plaindatetime
+description: Forwards error thrown by invoking "toString" property
+features: [Temporal]
+---*/
+
+var calendar = {
+  calendar: {
+    calendar: true,
+    toString: function() {
+      throw new Test262Error();
+    },
+  }
+};
+
+assert.throws(Test262Error, function() {
+  Temporal.now.plainDateTime(calendar);
+});
diff --git a/test/built-ins/Temporal/now/plainDateTime/calendar-object-fail-get-calendar.js b/test/built-ins/Temporal/now/plainDateTime/calendar-object-fail-get-calendar.js
new file mode 100644
index 0000000000..d9161a6a8e
--- /dev/null
+++ b/test/built-ins/Temporal/now/plainDateTime/calendar-object-fail-get-calendar.js
@@ -0,0 +1,17 @@
+// Copyright (C) 2021 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-temporal.now.plaindatetime
+description: Forwards error thrown by retrieving value of "calendar" property
+features: [Temporal]
+---*/
+
+var calendar = {
+  get calendar() {
+    throw new Test262Error();
+  },
+};
+
+assert.throws(Test262Error, function() {
+  Temporal.now.plainDateTime(calendar);
+});
diff --git a/test/built-ins/Temporal/now/plainDateTime/calendar-object-fail-has-calendar.js b/test/built-ins/Temporal/now/plainDateTime/calendar-object-fail-has-calendar.js
new file mode 100644
index 0000000000..c07d2308d1
--- /dev/null
+++ b/test/built-ins/Temporal/now/plainDateTime/calendar-object-fail-has-calendar.js
@@ -0,0 +1,20 @@
+// Copyright (C) 2021 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.now.plaindatetime
+description: Forwards error thrown by checking presence of "calendar" property
+features: [Temporal]
+---*/
+
+var calendar = new Proxy({}, {
+  has: function(target, property) {
+    if (property === 'calendar') {
+      throw new Test262Error();
+    }
+  },
+});
+
+assert.throws(Test262Error, function() {
+  Temporal.now.plainDateTime(calendar);
+});
diff --git a/test/built-ins/Temporal/now/plainDateTime/calendar-object-fail-has-nested-calendar.js b/test/built-ins/Temporal/now/plainDateTime/calendar-object-fail-has-nested-calendar.js
new file mode 100644
index 0000000000..f0d4c84858
--- /dev/null
+++ b/test/built-ins/Temporal/now/plainDateTime/calendar-object-fail-has-nested-calendar.js
@@ -0,0 +1,21 @@
+// Copyright (C) 2021 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-temporal.now.plaindatetime
+description: Forwards error thrown by checking presence of nested "calendar" property
+features: [Temporal]
+---*/
+
+var calendar = {
+  calendar: new Proxy({}, {
+    has: function(target, property) {
+      if (property === 'calendar') {
+        throw new Test262Error();
+      }
+    },
+  })
+};
+
+assert.throws(Test262Error, function() {
+  Temporal.now.plainDateTime(calendar);
+});
diff --git a/test/built-ins/Temporal/now/plainDateTime/calendar-object.js b/test/built-ins/Temporal/now/plainDateTime/calendar-object.js
new file mode 100644
index 0000000000..74a7dec849
--- /dev/null
+++ b/test/built-ins/Temporal/now/plainDateTime/calendar-object.js
@@ -0,0 +1,61 @@
+// Copyright (C) 2020 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.now.plaindatetime
+description: Observable interactions with the provided calendar-like object
+includes: [compareArray.js]
+features: [Temporal]
+---*/
+
+const actual = [];
+const expected = [
+  'has calendar.calendar',
+  'get calendar.calendar',
+  'has nestedCalendar.calendar',
+  'get nestedCalendar.Symbol(Symbol.toPrimitive)',
+  'get nestedCalendar.toString',
+  'call nestedCalendar.toString'
+];
+const nestedCalendar = new Proxy({
+  toString: function() {
+    actual.push('call nestedCalendar.toString');
+    return 'iso8601';
+  }
+}, {
+  has(target, property) {
+    actual.push(`has nestedCalendar.${String(property)}`);
+    return property in target;
+  },
+  get(target, property) {
+    actual.push(`get nestedCalendar.${String(property)}`);
+    return target[property];
+  },
+});
+const calendar = new Proxy({
+  calendar: nestedCalendar,
+  toString: function() {
+    actual.push('call calendar.toString');
+    return 'iso8601';
+  },
+}, {
+  has(target, property) {
+    actual.push(`has calendar.${String(property)}`);
+    return property in target;
+  },
+  get(target, property) {
+    actual.push(`get calendar.${String(property)}`);
+    return target[property];
+  },
+});
+
+Object.defineProperty(Temporal.Calendar, 'from', {
+  get() {
+    actual.push('get Temporal.Calendar.from');
+    return undefined;
+  },
+});
+
+Temporal.now.plainDateTime(calendar);
+
+assert.compareArray(actual, expected);
diff --git a/test/built-ins/Temporal/now/plainDateTime/calendar-temporal-object.js b/test/built-ins/Temporal/now/plainDateTime/calendar-temporal-object.js
new file mode 100644
index 0000000000..e3260accf8
--- /dev/null
+++ b/test/built-ins/Temporal/now/plainDateTime/calendar-temporal-object.js
@@ -0,0 +1,22 @@
+// Copyright (C) 2021 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.now.plaindatetime
+description: Fast path for converting other Temporal objects to Temporal.Calendar by reading internal slots
+info: |
+    sec-temporal.now.plaindatetime step 1:
+      1. Return ? SystemDateTime(_temporalTimeZoneLike_, _calendar_).
+    sec-temporal-systemdatetime step 3:
+      3. Let _calendar_ be ? ToTemporalCalendar(_calendarLike_).
+    sec-temporal-totemporalcalendar step 1.a:
+      a. If _temporalCalendarLike_ has an [[InitializedTemporalDate]], [[InitializedTemporalDateTime]], [[InitializedTemporalMonthDay]], [[InitializedTemporalYearMonth]], or [[InitializedTemporalZonedDateTime]] internal slot, then
+        i. Return _temporalCalendarLike_.[[Calendar]].
+includes: [compareArray.js, temporalHelpers.js]
+features: [Temporal]
+---*/
+
+TemporalHelpers.checkToTemporalCalendarFastPath((temporalObject, calendar) => {
+  const result = Temporal.now.plainDateTime(temporalObject);
+  assert.sameValue(result.calendar, calendar, "Temporal object coerced to calendar");
+});
diff --git a/test/built-ins/Temporal/now/plainDateTime/extensible.js b/test/built-ins/Temporal/now/plainDateTime/extensible.js
new file mode 100644
index 0000000000..85c91d80b0
--- /dev/null
+++ b/test/built-ins/Temporal/now/plainDateTime/extensible.js
@@ -0,0 +1,9 @@
+// Copyright (C) 2021 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-temporal.now.plaindatetime
+description: Temporal.now.plainDateTime is extensible.
+features: [Temporal]
+---*/
+
+assert(Object.isExtensible(Temporal.now.plainDateTime));
diff --git a/test/built-ins/Temporal/now/plainDateTime/length.js b/test/built-ins/Temporal/now/plainDateTime/length.js
new file mode 100644
index 0000000000..135faddbd3
--- /dev/null
+++ b/test/built-ins/Temporal/now/plainDateTime/length.js
@@ -0,0 +1,25 @@
+// Copyright (C) 2020 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.now.plaindatetime
+description: The `length` property of Temporal.now.plainDateTime
+info: |
+    Every built-in function object, including constructors, has a "length" property whose value is
+    an integer. Unless otherwise specified, this value is equal to the largest number of named
+    arguments shown in the subclause headings for the function description. Optional parameters
+    (which are indicated with brackets: [ ]) or rest parameters (which are shown using the form
+    «...name») are not included in the default argument count.
+
+    Unless otherwise specified, the "length" property of a built-in function object has the
+    attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.
+includes: [propertyHelper.js]
+features: [Temporal]
+---*/
+
+verifyProperty(Temporal.now.plainDateTime, "length", {
+  value: 1,
+  writable: false,
+  enumerable: false,
+  configurable: true,
+});
diff --git a/test/built-ins/Temporal/now/plainDateTime/name.js b/test/built-ins/Temporal/now/plainDateTime/name.js
new file mode 100644
index 0000000000..6b7818aa4f
--- /dev/null
+++ b/test/built-ins/Temporal/now/plainDateTime/name.js
@@ -0,0 +1,16 @@
+// Copyright (C) 2021 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-temporal.now.plainDateTime
+description: Temporal.now.plainDateTime.name is "plainDateTime".
+includes: [propertyHelper.js]
+features: [Temporal]
+---*/
+
+assert.sameValue(Temporal.now.plainDateTime.name, 'plainDateTime');
+
+verifyProperty(Temporal.now.plainDateTime, 'name', {
+  enumerable: false,
+  writable: false,
+  configurable: true
+});
diff --git a/test/built-ins/Temporal/now/plainDateTime/not-a-constructor.js b/test/built-ins/Temporal/now/plainDateTime/not-a-constructor.js
new file mode 100644
index 0000000000..4f8f19ac4d
--- /dev/null
+++ b/test/built-ins/Temporal/now/plainDateTime/not-a-constructor.js
@@ -0,0 +1,14 @@
+// Copyright (C) 2021 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-temporal.now.plaindatetime
+description: Temporal.now.plainDateTime does not implement [[Construct]]
+includes: [isConstructor.js]
+features: [Reflect.construct, Temporal]
+---*/
+
+assert.sameValue(isConstructor(Temporal.now.plainDateTime), false, 'isConstructor(Temporal.now.plainDateTime) must return false');
+
+assert.throws(TypeError, () => {
+  new Temporal.now.plainDateTime();
+}, '`new Temporal.now.plainDateTime()` throws TypeError');
diff --git a/test/built-ins/Temporal/now/plainDateTime/prop-desc.js b/test/built-ins/Temporal/now/plainDateTime/prop-desc.js
new file mode 100644
index 0000000000..d2dfb0d282
--- /dev/null
+++ b/test/built-ins/Temporal/now/plainDateTime/prop-desc.js
@@ -0,0 +1,14 @@
+// Copyright (C) 2021 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-temporal.now.plaindatetime
+description: The "plainDateTime" property of Temporal.now
+includes: [propertyHelper.js]
+features: [Temporal]
+---*/
+
+verifyProperty(Temporal.now, 'plainDateTime', {
+  enumerable: false,
+  writable: true,
+  configurable: true
+});
diff --git a/test/built-ins/Temporal/now/plainDateTime/return-value.js b/test/built-ins/Temporal/now/plainDateTime/return-value.js
new file mode 100644
index 0000000000..e0258586ce
--- /dev/null
+++ b/test/built-ins/Temporal/now/plainDateTime/return-value.js
@@ -0,0 +1,20 @@
+// Copyright (C) 2020 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.now.plaindatetime
+description: Return value describes the start of a day
+features: [Temporal]
+---*/
+
+const calendar = Temporal.Calendar.from("iso8601");
+const timeZone = {
+  getOffsetNanosecondsFor(instant) {
+    return -Number(instant.epochNanoseconds % 86400_000_000_000n);
+  }
+};
+
+const result = Temporal.now.plainDateTime(calendar, timeZone);
+for (const property of ["hour", "minute", "second", "millisecond", "microsecond", "nanosecond"]) {
+  assert.sameValue(result[property], 0, property);
+}
diff --git a/test/built-ins/Temporal/now/plainDateTime/time-zone-undefined.js b/test/built-ins/Temporal/now/plainDateTime/time-zone-undefined.js
new file mode 100644
index 0000000000..43d6a286c1
--- /dev/null
+++ b/test/built-ins/Temporal/now/plainDateTime/time-zone-undefined.js
@@ -0,0 +1,29 @@
+// Copyright (C) 2021 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.now.plaindatetime
+description: Functions when time zone argument is omitted
+includes: [compareArray.js]
+features: [Temporal]
+---*/
+
+const actual = [];
+const expected = [];
+
+Object.defineProperty(Temporal.TimeZone, "from", {
+  get() {
+    actual.push("get Temporal.TimeZone.from");
+    return undefined;
+  },
+});
+
+const resultExplicit = Temporal.now.plainDateTime("iso8601", undefined);
+assert(resultExplicit instanceof Temporal.PlainDateTime);
+
+assert.compareArray(actual, expected, "Temporal.TimeZone.from should not be called");
+
+const resultImplicit = Temporal.now.plainDateTime("iso8601");
+assert(resultImplicit instanceof Temporal.PlainDateTime);
+
+assert.compareArray(actual, expected, "Temporal.TimeZone.from should not be called");
diff --git a/test/built-ins/Temporal/now/plainDateTime/timezone-getoffsetnanosecondsfor-invocation.js b/test/built-ins/Temporal/now/plainDateTime/timezone-getoffsetnanosecondsfor-invocation.js
new file mode 100644
index 0000000000..0fe33230d8
--- /dev/null
+++ b/test/built-ins/Temporal/now/plainDateTime/timezone-getoffsetnanosecondsfor-invocation.js
@@ -0,0 +1,25 @@
+// Copyright (C) 2021 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-temporal.now.plaindatetime
+description: Correctly invokes `getOffsetNanosecondsFor` method of TimeZone-like objects
+features: [Temporal]
+---*/
+
+var calls = [];
+var timeZone = {
+  getOffsetNanosecondsFor: function() {
+    calls.push({
+      args: arguments,
+      this: this
+    });
+    return 0;
+  },
+};
+
+Temporal.now.plainDateTime('iso8601', timeZone);
+
+assert.sameValue(calls.length, 1, 'call count');
+assert.sameValue(calls[0].args.length, 1, 'arguments');
+assert(calls[0].args[0] instanceof Temporal.Instant);
+assert.sameValue(calls[0].this, timeZone);
diff --git a/test/built-ins/Temporal/now/plainDateTime/timezone-getoffsetnanosecondsfor-non-integer.js b/test/built-ins/Temporal/now/plainDateTime/timezone-getoffsetnanosecondsfor-non-integer.js
new file mode 100644
index 0000000000..b18f8c2228
--- /dev/null
+++ b/test/built-ins/Temporal/now/plainDateTime/timezone-getoffsetnanosecondsfor-non-integer.js
@@ -0,0 +1,15 @@
+// Copyright (C) 2021 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.now.plaindatetime
+description: RangeError thrown if time zone reports an offset that is not an integer number of nanoseconds
+features: [Temporal]
+includes: [temporalHelpers.js]
+---*/
+
+[3600_000_000_000.5, NaN].forEach((wrongOffset) => {
+  const timeZone = TemporalHelpers.specificOffsetTimeZone(wrongOffset);
+
+  assert.throws(RangeError, () => Temporal.now.plainDateTime("iso8601", timeZone));
+});
diff --git a/test/built-ins/Temporal/now/plainDateTime/timezone-getoffsetnanosecondsfor-non-method.js b/test/built-ins/Temporal/now/plainDateTime/timezone-getoffsetnanosecondsfor-non-method.js
new file mode 100644
index 0000000000..f35f30bdd1
--- /dev/null
+++ b/test/built-ins/Temporal/now/plainDateTime/timezone-getoffsetnanosecondsfor-non-method.js
@@ -0,0 +1,15 @@
+// Copyright (C) 2021 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-temporal.now.plaindatetime
+description: Rejects when `getOffsetNanosecondsFor` property is not a method
+features: [Temporal]
+---*/
+
+var timeZone = {
+  getOffsetNanosecondsFor: 7
+};
+
+assert.throws(TypeError, function() {
+  Temporal.now.plainDateTime('iso8601', timeZone);
+});
diff --git a/test/built-ins/Temporal/now/plainDateTime/timezone-getoffsetnanosecondsfor-not-a-number.js b/test/built-ins/Temporal/now/plainDateTime/timezone-getoffsetnanosecondsfor-not-a-number.js
new file mode 100644
index 0000000000..d080e76ab4
--- /dev/null
+++ b/test/built-ins/Temporal/now/plainDateTime/timezone-getoffsetnanosecondsfor-not-a-number.js
@@ -0,0 +1,33 @@
+// Copyright (C) 2020 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.now.plaindatetime
+description: Rejects non-numeric nanosecond values reported by TimeZone-like object
+features: [Temporal]
+---*/
+
+const invalidValues = [
+  undefined,
+  null,
+  true,
+  "2020-01-01T12:45:36",
+  Symbol(),
+  2n,
+  {},
+  Temporal.PlainDateTime,
+  Temporal.PlainDateTime.prototype,
+];
+
+for (const dateTime of invalidValues) {
+  let callCount = 0;
+  const timeZone = {
+    getOffsetNanosecondsFor(instant, calendar) {
+      callCount += 1;
+      return dateTime;
+    },
+  };
+
+  assert.throws(TypeError, () => Temporal.now.plainDateTime("iso8601", timeZone));
+  assert.sameValue(callCount, 1, 'Invoked `getOffsetNanosecondsFor`');
+}
diff --git a/test/built-ins/Temporal/now/plainDateTime/timezone-getoffsetnanosecondsfor-out-of-range.js b/test/built-ins/Temporal/now/plainDateTime/timezone-getoffsetnanosecondsfor-out-of-range.js
new file mode 100644
index 0000000000..ba14c11cff
--- /dev/null
+++ b/test/built-ins/Temporal/now/plainDateTime/timezone-getoffsetnanosecondsfor-out-of-range.js
@@ -0,0 +1,15 @@
+// Copyright (C) 2021 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.now.plaindatetime
+description: RangeError thrown if time zone reports an offset that is out of range
+features: [Temporal]
+includes: [temporalHelpers.js]
+---*/
+
+[-86400_000_000_001, 86400_000_000_001, -Infinity, Infinity].forEach((wrongOffset) => {
+  const timeZone = TemporalHelpers.specificOffsetTimeZone(wrongOffset);
+
+  assert.throws(RangeError, () => Temporal.now.plainDateTime("iso8601", timeZone));
+});
diff --git a/test/built-ins/Temporal/now/plainDateTime/timezone-getoffsetnanosecondsfor-poisoned.js b/test/built-ins/Temporal/now/plainDateTime/timezone-getoffsetnanosecondsfor-poisoned.js
new file mode 100644
index 0000000000..b0780d260a
--- /dev/null
+++ b/test/built-ins/Temporal/now/plainDateTime/timezone-getoffsetnanosecondsfor-poisoned.js
@@ -0,0 +1,17 @@
+// Copyright (C) 2021 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-temporal.now.plaindatetime
+description: Forwards error when accessing `getOffsetNanosecondsFor` property throws
+features: [Temporal]
+---*/
+
+var timeZone = {
+  get getOffsetNanosecondsFor() {
+    throw new Test262Error();
+  }
+};
+
+assert.throws(Test262Error, function() {
+  Temporal.now.plainDateTime('iso8601', timeZone);
+});
diff --git a/test/built-ins/Temporal/now/plainDateTime/timezone-getoffsetnanosecondsfor-throws.js b/test/built-ins/Temporal/now/plainDateTime/timezone-getoffsetnanosecondsfor-throws.js
new file mode 100644
index 0000000000..8bef0b8482
--- /dev/null
+++ b/test/built-ins/Temporal/now/plainDateTime/timezone-getoffsetnanosecondsfor-throws.js
@@ -0,0 +1,17 @@
+// Copyright (C) 2021 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-temporal.now.plaindatetime
+description: Forwards error when `getOffsetNanosecondsFor` throws
+features: [Temporal]
+---*/
+
+var timeZone = {
+  getOffsetNanosecondsFor() {
+    throw new Test262Error();
+  }
+};
+
+assert.throws(Test262Error, function() {
+  Temporal.now.plainDateTime('iso8601', timeZone);
+});
diff --git a/test/built-ins/Temporal/now/plainDateTime/timezone-getoffsetnanosecondsfor-wrong-type.js b/test/built-ins/Temporal/now/plainDateTime/timezone-getoffsetnanosecondsfor-wrong-type.js
new file mode 100644
index 0000000000..89b06145f9
--- /dev/null
+++ b/test/built-ins/Temporal/now/plainDateTime/timezone-getoffsetnanosecondsfor-wrong-type.js
@@ -0,0 +1,24 @@
+// Copyright (C) 2021 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.now.plaindatetime
+description: TypeError thrown if time zone reports an offset that is not a Number
+features: [Temporal]
+includes: [temporalHelpers.js]
+---*/
+
+[
+  undefined,
+  null,
+  true,
+  "+01:00",
+  Symbol(),
+  3600_000_000_000n,
+  {},
+  { valueOf() { return 3600_000_000_000; } },
+].forEach((wrongOffset) => {
+  const timeZone = TemporalHelpers.specificOffsetTimeZone(wrongOffset);
+
+  assert.throws(TypeError, () => Temporal.now.plainDateTime("iso8601", timeZone));
+});
diff --git a/test/built-ins/Temporal/now/plainDateTime/timezone-object-fail-call-tostring.js b/test/built-ins/Temporal/now/plainDateTime/timezone-object-fail-call-tostring.js
new file mode 100644
index 0000000000..6d6c18111f
--- /dev/null
+++ b/test/built-ins/Temporal/now/plainDateTime/timezone-object-fail-call-tostring.js
@@ -0,0 +1,20 @@
+// Copyright (C) 2021 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-temporal.now.plaindatetime
+description: Forwards error thrown by invoking "toString" property
+features: [Temporal]
+---*/
+
+var timeZone = {
+  timeZone: {
+    timeZone: true,
+    toString: function() {
+      throw new Test262Error();
+    },
+  }
+};
+
+assert.throws(Test262Error, function() {
+  Temporal.now.plainDateTime("iso8601", timeZone);
+});
diff --git a/test/built-ins/Temporal/now/plainDateTime/timezone-object-fail-get-timezone.js b/test/built-ins/Temporal/now/plainDateTime/timezone-object-fail-get-timezone.js
new file mode 100644
index 0000000000..98a0d91423
--- /dev/null
+++ b/test/built-ins/Temporal/now/plainDateTime/timezone-object-fail-get-timezone.js
@@ -0,0 +1,17 @@
+// Copyright (C) 2021 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-temporal.now.plaindatetime
+description: Forwards error thrown by retrieving value of "timeZone" property
+features: [Temporal]
+---*/
+
+var timeZone = {
+  get timeZone() {
+    throw new Test262Error();
+  },
+};
+
+assert.throws(Test262Error, function() {
+  Temporal.now.plainDateTime("iso8601", timeZone);
+});
diff --git a/test/built-ins/Temporal/now/plainDateTime/timezone-object-fail-has-nested-timezone.js b/test/built-ins/Temporal/now/plainDateTime/timezone-object-fail-has-nested-timezone.js
new file mode 100644
index 0000000000..61d3540d6a
--- /dev/null
+++ b/test/built-ins/Temporal/now/plainDateTime/timezone-object-fail-has-nested-timezone.js
@@ -0,0 +1,21 @@
+// Copyright (C) 2021 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-temporal.now.plaindatetime
+description: Forwards error thrown by checking presence of nested "timeZone" property
+features: [Temporal]
+---*/
+
+var timeZone = {
+  timeZone: new Proxy({}, {
+    has: function(target, property) {
+      if (property === 'timeZone') {
+        throw new Test262Error();
+      }
+    },
+  })
+};
+
+assert.throws(Test262Error, function() {
+  Temporal.now.plainDateTime("iso8601", timeZone);
+});
diff --git a/test/built-ins/Temporal/now/plainDateTime/timezone-object-fail-has-timezone.js b/test/built-ins/Temporal/now/plainDateTime/timezone-object-fail-has-timezone.js
new file mode 100644
index 0000000000..da56d1ed21
--- /dev/null
+++ b/test/built-ins/Temporal/now/plainDateTime/timezone-object-fail-has-timezone.js
@@ -0,0 +1,19 @@
+// Copyright (C) 2021 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-temporal.now.plaindatetime
+description: Forwards error thrown by checking presence of "timeZone" property
+features: [Temporal]
+---*/
+
+var timeZone = new Proxy({}, {
+  has: function(target, property) {
+    if (property === 'timeZone') {
+      throw new Test262Error();
+    }
+  },
+});
+
+assert.throws(Test262Error, function() {
+  Temporal.now.plainDateTime("iso8601", timeZone);
+});
diff --git a/test/built-ins/Temporal/now/plainDateTime/timezone-object.js b/test/built-ins/Temporal/now/plainDateTime/timezone-object.js
new file mode 100644
index 0000000000..381f47b634
--- /dev/null
+++ b/test/built-ins/Temporal/now/plainDateTime/timezone-object.js
@@ -0,0 +1,62 @@
+// Copyright (C) 2020 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.now.plaindatetime
+description: Observable interactions with the provided timezone-like object
+includes: [compareArray.js]
+features: [Temporal]
+---*/
+
+const actual = [];
+const expected = [
+  "has timeZone.timeZone",
+  "get timeZone.timeZone",
+  "has nestedTimeZone.timeZone",
+  "get nestedTimeZone.getOffsetNanosecondsFor",
+  "call nestedTimeZone.getOffsetNanosecondsFor",
+];
+const nestedTimeZone = new Proxy({
+  getOffsetNanosecondsFor(instant) {
+    actual.push("call nestedTimeZone.getOffsetNanosecondsFor");
+    assert.sameValue(instant instanceof Temporal.Instant, true, "Instant");
+    return -Number(instant.epochNanoseconds % 86400_000_000_000n);
+  },
+}, {
+  has(target, property) {
+    actual.push(`has nestedTimeZone.${String(property)}`);
+    return property in target;
+  },
+  get(target, property) {
+    actual.push(`get nestedTimeZone.${String(property)}`);
+    return target[property];
+  },
+});
+const timeZone = new Proxy({
+  timeZone: nestedTimeZone,
+  getOffsetNanosecondsFor(instant) {
+    actual.push("call timeZone.getOffsetNanosecondsFor");
+    assert.sameValue(instant instanceof Temporal.Instant, true, "Instant");
+    return -Number(instant.epochNanoseconds % 86400_000_000_000n);
+  },
+}, {
+  has(target, property) {
+    actual.push(`has timeZone.${property}`);
+    return property in target;
+  },
+  get(target, property) {
+    actual.push(`get timeZone.${property}`);
+    return target[property];
+  },
+});
+
+Object.defineProperty(Temporal.TimeZone, "from", {
+  get() {
+    actual.push("get Temporal.TimeZone.from");
+    return undefined;
+  },
+});
+
+Temporal.now.plainDateTime("iso8601", timeZone);
+
+assert.compareArray(actual, expected);