add `Error.isError` tests

See https://github.com/tc39/proposal-is-error/issues/7

test/built-ins/Error/isError/bigints.js

@@ -0,0 +1,14 @@
+// Copyright (C) 2024 Jordan Harband.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-error.iserror
+description: >
+  Returns false on bigints
+features: [BigInt]
+---*/
+
+assert.sameValue(Error.isError(0n), false);
+assert.sameValue(Error.isError(42n), false);
+assert.sameValue(Error.isError(new BigInt(0)), false);
+assert.sameValue(Error.isError(new BigInt(42)), false);

test/built-ins/Error/isError/error-subclass.js

@@ -0,0 +1,37 @@
+// Copyright (C) 2024 Jordan Harband.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-error.iserror
+description: >
+  Returns true on userland Error subclasses
+features: [class]
+---*/
+
+class MyError extends Error {}
+class MyEvalError extends EvalError {}
+class MyRangeError extends RangeError {}
+class MyReferenceError extends ReferenceError {}
+class MySyntaxError extends SyntaxError {}
+class MyTypeError extends TypeError {}
+class MyURIError extends URIError {}
+
+assert.sameValue(Error.isError(new MyError()), true);
+assert.sameValue(Error.isError(new MyEvalError()), true);
+assert.sameValue(Error.isError(new MyRangeError()), true);
+assert.sameValue(Error.isError(new MyReferenceError()), true);
+assert.sameValue(Error.isError(new MySyntaxError()), true);
+assert.sameValue(Error.isError(new MyTypeError()), true);
+assert.sameValue(Error.isError(new MyURIError()), true);
+
+if (typeof AggregateError !== 'undefined') {
+  class MyAggregateError extends AggregateError {}
+
+  assert.sameValue(Error.isError(new MyAggregateError()), true);
+}
+
+if (typeof SuppressedError !== 'undefined') {
+  class MySuppressedError extends SuppressedError {}
+
+  assert.sameValue(Error.isError(new MySuppressedError()), true);
+}

test/built-ins/Error/isError/errors-other-realm.js

@@ -0,0 +1,26 @@
+// Copyright (C) 2024 Jordan Harband.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-error.iserror
+description: >
+  Returns true on Error and Error subclass instances from a different realm
+features: [cross-realm]
+---*/
+
+var other = $262.createRealm().global;
+
+assert.sameValue(Error.isError(new other.Error()), true);
+assert.sameValue(Error.isError(new other.EvalError()), true);
+assert.sameValue(Error.isError(new other.RangeError()), true);
+assert.sameValue(Error.isError(new other.ReferenceError()), true);
+assert.sameValue(Error.isError(new other.SyntaxError()), true);
+assert.sameValue(Error.isError(new other.TypeError()), true);
+assert.sameValue(Error.isError(new other.URIError()), true);
+
+if (typeof AggregateError !== 'undefined') {
+  assert.sameValue(Error.isError(new other.AggregateError()), true);
+}
+if (typeof SuppressedError !== 'undefined') {
+  assert.sameValue(Error.isError(new other.SuppressedError()), true);
+}

test/built-ins/Error/isError/errors.js

@@ -0,0 +1,23 @@
+// Copyright (C) 2024 Jordan Harband.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-error.iserror
+description: >
+  Returns true on Error and Error subclass instances
+---*/
+
+assert.sameValue(Error.isError(new Error()), true);
+assert.sameValue(Error.isError(new EvalError()), true);
+assert.sameValue(Error.isError(new RangeError()), true);
+assert.sameValue(Error.isError(new ReferenceError()), true);
+assert.sameValue(Error.isError(new SyntaxError()), true);
+assert.sameValue(Error.isError(new TypeError()), true);
+assert.sameValue(Error.isError(new URIError()), true);
+
+if (typeof AggregateError !== 'undefined') {
+  assert.sameValue(Error.isError(new AggregateError()), true);
+}
+if (typeof SuppressedError !== 'undefined') {
+  assert.sameValue(Error.isError(new SuppressedError()), true);
+}

test/built-ins/Error/isError/fake-errors.js

@@ -0,0 +1,21 @@
+// Copyright (C) 2024 Jordan Harband.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-error.iserror
+description: >
+  Returns false on non-Error objects pretending to be an Error
+---*/
+
+var fakeError = {
+  __proto__: Error.prototype,
+  constructor: Error,
+  message: '',
+  stack: new Error().stack
+};
+
+if (typeof Symbol === 'function' && typeof Symbol.toStringTag === 'symbol') {
+  fakeError[Symbol.toStringTag] = 'Error';
+}
+
+assert.sameValue(Error.isError(fakeError), false);

test/built-ins/Error/isError/is-a-constructor.js

@@ -0,0 +1,24 @@
+// Copyright (C) 2024 Jordan Harband. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-error.iserror
+description: >
+  Error.isError does not implement [[Construct]]
+info: |
+  IsConstructor ( argument )
+
+  The abstract operation IsConstructor takes argument argument (an ECMAScript language value).
+  It determines if argument is a function object with a [[Construct]] internal method.
+  It performs the following steps when called:
+
+  If Type(argument) is not Object, return false.
+  If argument has a [[Construct]] internal method, return true.
+  Return false.
+includes: [isConstructor.js]
+features: [Reflect.construct]
+---*/
+
+assert.sameValue(isConstructor(Error.isError), false, 'isConstructor(Error.isError) must return false');
+assert.throws(TypeError, function () { new Error.isError(); });
+

test/built-ins/Error/isError/name.js

@@ -0,0 +1,11 @@
+// Copyright (C) 2024 Jordan Harband.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-error.iserror
+description: >
+  The initial value of Error.isError.name is "isError".
+---*/
+
+assert.sameValue(Error.isError.name, 'isError');
+

test/built-ins/Error/isError/non-error-objects-other-realm.js

@@ -0,0 +1,31 @@
+// Copyright (C) 2024 Jordan Harband.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-error.iserror
+description: >
+  Returns false on non-Error objects from a different realm
+features: [cross-realm]
+---*/
+
+var other = $262.createRealm().global;
+
+assert.sameValue(Error.isError(new other.Object()), false);
+assert.sameValue(Error.isError(new other.Array()), false);
+assert.sameValue(Error.isError(new other.Function('')), false);
+assert.sameValue(Error.isError(new other.RegExp('a')), false);
+
+assert.sameValue(Error.isError(other.Error), false);
+assert.sameValue(Error.isError(other.EvalError), false);
+assert.sameValue(Error.isError(other.RangeError), false);
+assert.sameValue(Error.isError(other.ReferenceError), false);
+assert.sameValue(Error.isError(other.SyntaxError), false);
+assert.sameValue(Error.isError(other.TypeError), false);
+assert.sameValue(Error.isError(other.URIError), false);
+
+if (typeof other.AggregateError !== 'undefined') {
+  assert.sameValue(Error.isError(other.AggregateError), false);
+}
+if (typeof other.SuppressedError !== 'undefined') {
+  assert.sameValue(Error.isError(other.SuppressedError), false);
+}

test/built-ins/Error/isError/non-error-objects.js

@@ -0,0 +1,28 @@
+// Copyright (C) 2024 Jordan Harband.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-error.iserror
+description: >
+  Returns false on non-Error objects
+---*/
+
+assert.sameValue(Error.isError({}), false);
+assert.sameValue(Error.isError([]), false);
+assert.sameValue(Error.isError(function () {}), false);
+assert.sameValue(Error.isError(/a/g), false);
+
+assert.sameValue(Error.isError(Error), false);
+assert.sameValue(Error.isError(EvalError), false);
+assert.sameValue(Error.isError(RangeError), false);
+assert.sameValue(Error.isError(ReferenceError), false);
+assert.sameValue(Error.isError(SyntaxError), false);
+assert.sameValue(Error.isError(TypeError), false);
+assert.sameValue(Error.isError(URIError), false);
+
+if (typeof AggregateError !== 'undefined') {
+  assert.sameValue(Error.isError(AggregateError), false);
+}
+if (typeof SuppressedError !== 'undefined') {
+  assert.sameValue(Error.isError(SuppressedError), false);
+}

test/built-ins/Error/isError/primitives.js

@@ -0,0 +1,22 @@
+// Copyright (C) 2024 Jordan Harband.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-error.iserror
+description: >
+  Returns false on primitives
+---*/
+
+assert.sameValue(Error.isError(), false);
+assert.sameValue(Error.isError(undefined), false);
+assert.sameValue(Error.isError(null), false);
+assert.sameValue(Error.isError(true), false);
+assert.sameValue(Error.isError(false), false);
+assert.sameValue(Error.isError(0), false);
+assert.sameValue(Error.isError(-0), false);
+assert.sameValue(Error.isError(NaN), false);
+assert.sameValue(Error.isError(Infinity), false);
+assert.sameValue(Error.isError(-Infinity), false);
+assert.sameValue(Error.isError(42), false);
+assert.sameValue(Error.isError(''), false);
+assert.sameValue(Error.isError('foo'), false);

test/built-ins/Error/isError/prop-desc.js

@@ -0,0 +1,18 @@
+// Copyright (C) 2024 Jordan Harband. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-error.iserror
+description: Property descriptor for Error.isError
+info: |
+  Every other data property described in clauses 18 through 26 and in Annex B.2
+  has the attributes { [[Writable]]: true, [[Enumerable]]: false,
+  [[Configurable]]: true } unless otherwise specified.
+includes: [propertyHelper.js]
+---*/
+
+verifyProperty(Error, "isError", {
+  writable: true,
+  enumerable: false,
+  configurable: true
+});

test/built-ins/Error/isError/symbols.js

@@ -0,0 +1,11 @@
+// Copyright (C) 2024 Jordan Harband.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-error.iserror
+description: >
+  Returns false on symbols
+features: [Symbol]
+---*/
+
+assert.sameValue(Error.isError(new Symbol()), false);