text: // Copyright (C) 2017 Ecma International.  All rights reserved.
  // This code is governed by the BSD license found in the LICENSE file.
  /*---
  description: |
      Collection of assertion functions used throughout test262
  defines: [assert]
  ---*/
  
  
  function assert(mustBeTrue, message) {
      if (mustBeTrue === true) {
          return;
      }
  
      if (message === undefined) {
          message = 'Expected true but got ' + assert._toString(mustBeTrue);
      }
      throw (message);
  }
  
  assert._isSameValue = function (a, b) {
      if (a === b) {
          // Handle +/-0 vs. -/+0
          return a !== 0 || 1 / a === 1 / b;
      }
  
      // Handle NaN vs. NaN
      return a !== a && b !== b;
  };
  
  assert.sameValue = function (actual, expected, message) {
      try {
          if (assert._isSameValue(actual, expected)) {
              return;
          }
      } catch (error) {
          throw (message + ' (_isSameValue operation threw) ' + error);
      }
  
      if (message === undefined) {
          message = '';
      } else {
          message += ' ';
      }
  
      message += 'Expected SameValue(«' + assert._toString(actual) + '», «' + assert._toString(expected) + '») to be true';
  
      throw (message);
  };
  
  assert.notSameValue = function (actual, unexpected, message) {
      if (!assert._isSameValue(actual, unexpected)) {
          return;
      }
  
      if (message === undefined) {
          message = '';
      } else {
          message += ' ';
      }
  
      message += 'Expected SameValue(«' + assert._toString(actual) + '», «' + assert._toString(unexpected) + '») to be false';
  
      throw (message);
  };
  
  assert.throws = function (expectedErrorConstructor, func, message) {
      if (typeof func !== "function") {
          throw ('assert.throws requires two arguments: the error constructor ' +
              'and a function to run');
      }
      if (message === undefined) {
          message = '';
      } else {
          message += ' ';
      }
  
      try {
          func();
      } catch (thrown) {
          if (typeof thrown !== 'object' || thrown === null) {
              message += 'Thrown value was not an object!';
              throw (message);
          } else if (thrown.constructor !== expectedErrorConstructor) {
              message += 'Expected a ' + expectedErrorConstructor.name + ' but got a ' + thrown.constructor.name;
              throw (message);
          }
          return;
      }
  
      message += 'Expected a ' + expectedErrorConstructor.name + ' to be thrown but no exception was thrown at all';
      throw (message);
  };
  
  assert._toString = function (value) {
      try {
          if (value === 0 && 1 / value === -Infinity) {
              return '-0';
          }
  
          return String(value);
      } catch (err) {
          if (err.name === 'TypeError') {
              return Object.prototype.toString.call(value);
          }
  
          throw err;
      }
  };
  
  // Copyright (C) 2017 Ecma International.  All rights reserved.
  // This code is governed by the BSD license found in the LICENSE file.
  /*---
  description: |
      Collection of functions used to safely verify the correctness of
      property descriptors.
  defines:
    - verifyProperty
    - verifyEqualTo
    - verifyWritable
    - verifyNotWritable
    - verifyEnumerable
    - verifyNotEnumerable
    - verifyConfigurable
    - verifyNotConfigurable
  ---*/
  
  // @ts-check
  
  /**
   * @param {object} obj
   * @param {string|symbol} name
   * @param {PropertyDescriptor|undefined} desc
   * @param {object} [options]
   * @param {boolean} [options.restore]
   */
  function verifyProperty(obj, name, desc, options) {
      assert(
          arguments.length > 2,
          'verifyProperty should receive at least 3 arguments: obj, name, and descriptor'
      );
  
      var originalDesc = Object.getOwnPropertyDescriptor(obj, name);
      var nameStr = String(name);
  
      // Allows checking for undefined descriptor if it's explicitly given.
      if (desc === undefined) {
          assert.sameValue(
              originalDesc,
              undefined,
              "obj['" + nameStr + "'] descriptor should be undefined"
          );
  
          // desc and originalDesc are both undefined, problem solved;
          return true;
      }
  
      assert(
          Object.prototype.hasOwnProperty.call(obj, name),
          "obj should have an own property " + nameStr
      );
  
      assert.notSameValue(
          desc,
          null,
          "The desc argument should be an object or undefined, null"
      );
  
      assert.sameValue(
          typeof desc,
          "object",
          "The desc argument should be an object or undefined, " + String(desc)
      );
  
      var failures = [];
  
      if (Object.prototype.hasOwnProperty.call(desc, 'value')) {
          if (!isSameValue(desc.value, originalDesc.value)) {
              failures.push("descriptor value should be " + desc.value);
          }
      }
  
      if (Object.prototype.hasOwnProperty.call(desc, 'enumerable')) {
          if (desc.enumerable !== originalDesc.enumerable ||
              desc.enumerable !== isEnumerable(obj, name)) {
              failures.push('descriptor should ' + (desc.enumerable ? '' : 'not ') + 'be enumerable');
          }
      }
  
      if (Object.prototype.hasOwnProperty.call(desc, 'writable')) {
          if (desc.writable !== originalDesc.writable ||
              desc.writable !== isWritable(obj, name)) {
              failures.push('descriptor should ' + (desc.writable ? '' : 'not ') + 'be writable');
          }
      }
  
      if (Object.prototype.hasOwnProperty.call(desc, 'configurable')) {
          if (desc.configurable !== originalDesc.configurable ||
              desc.configurable !== isConfigurable(obj, name)) {
              failures.push('descriptor should ' + (desc.configurable ? '' : 'not ') + 'be configurable');
          }
      }
  
      assert(!failures.length, failures.join('; '));
  
      if (options && options.restore) {
          Object.defineProperty(obj, name, originalDesc);
      }
  
      return true;
  }
  
  function isConfigurable(obj, name) {
      var hasOwnProperty = Object.prototype.hasOwnProperty;
      try {
          delete obj[name];
      } catch (e) {
          if (!(e instanceof TypeError)) {
              throw ("Expected TypeError, got " + e)
          }
      }
      return !hasOwnProperty.call(obj, name);
  }
  
  function isEnumerable(obj, name) {
      var stringCheck = false;
  
      if (typeof name === "string") {
          for (var x in obj) {
              if (x === name) {
                  stringCheck = true;
                  break;
              }
          }
      } else {
          // skip it if name is not string, works for Symbol names.
          stringCheck = true;
      }
  
      return stringCheck &&
          Object.prototype.hasOwnProperty.call(obj, name) &&
          Object.prototype.propertyIsEnumerable.call(obj, name);
  }
  
  function isSameValue(a, b) {
      if (a === 0 && b === 0) return 1 / a === 1 / b;
      if (a !== a && b !== b) return true;
  
      return a === b;
  }
  
  var __isArray = Array.isArray;
  function isWritable(obj, name, verifyProp, value) {
      var unlikelyValue = __isArray(obj) && name === "length" ?
          Math.pow(2, 32) - 1 :
          "unlikelyValue";
      var newValue = value || unlikelyValue;
      var hadValue = Object.prototype.hasOwnProperty.call(obj, name);
      var oldValue = obj[name];
      var writeSucceeded;
  
      try {
          obj[name] = newValue;
      } catch (e) {
          if (!(e instanceof TypeError)) {
              throw ("Expected TypeError, got " + e);
          }
      }
  
      writeSucceeded = isSameValue(obj[verifyProp || name], newValue);
  
      // Revert the change only if it was successful (in other cases, reverting
      // is unnecessary and may trigger exceptions for certain property
      // configurations)
      if (writeSucceeded) {
          if (hadValue) {
              obj[name] = oldValue;
          } else {
              delete obj[name];
          }
      }
  
      return writeSucceeded;
  }
  
  function verifyEqualTo(obj, name, value) {
      if (!isSameValue(obj[name], value)) {
          throw ("Expected obj[" + String(name) + "] to equal " + value +
              ", actually " + obj[name]);
      }
  }
  
  function verifyWritable(obj, name, verifyProp, value) {
      if (!verifyProp) {
          assert(Object.getOwnPropertyDescriptor(obj, name).writable,
              "Expected obj[" + String(name) + "] to have writable:true.");
      }
      if (!isWritable(obj, name, verifyProp, value)) {
          throw ("Expected obj[" + String(name) + "] to be writable, but was not.");
      }
  }
  
  function verifyNotWritable(obj, name, verifyProp, value) {
      if (!verifyProp) {
          assert(!Object.getOwnPropertyDescriptor(obj, name).writable,
              "Expected obj[" + String(name) + "] to have writable:false.");
      }
      if (isWritable(obj, name, verifyProp)) {
          throw ("Expected obj[" + String(name) + "] NOT to be writable, but was.");
      }
  }
  
  function verifyEnumerable(obj, name) {
      assert(Object.getOwnPropertyDescriptor(obj, name).enumerable,
          "Expected obj[" + String(name) + "] to have enumerable:true.");
      if (!isEnumerable(obj, name)) {
          throw ("Expected obj[" + String(name) + "] to be enumerable, but was not.");
      }
  }
  
  function verifyNotEnumerable(obj, name) {
      assert(!Object.getOwnPropertyDescriptor(obj, name).enumerable,
          "Expected obj[" + String(name) + "] to have enumerable:false.");
      if (isEnumerable(obj, name)) {
          throw ("Expected obj[" + String(name) + "] NOT to be enumerable, but was.");
      }
  }
  
  function verifyConfigurable(obj, name) {
      assert(Object.getOwnPropertyDescriptor(obj, name).configurable,
          "Expected obj[" + String(name) + "] to have configurable:true.");
      if (!isConfigurable(obj, name)) {
          throw ("Expected obj[" + String(name) + "] to be configurable, but was not.");
      }
  }
  
  function verifyNotConfigurable(obj, name) {
      assert(!Object.getOwnPropertyDescriptor(obj, name).configurable,
          "Expected obj[" + String(name) + "] to have configurable:false.");
      if (isConfigurable(obj, name)) {
          throw ("Expected obj[" + String(name) + "] NOT to be configurable, but was.");
      }
  }
  
  function Test262Error(message) {
      this.message = message || "";
  }
  
  Test262Error.prototype.toString = function () {
      return "Test262Error: " + this.message;
  };
  // This file was procedurally generated from the following sources:
  // - src/dstr-binding/obj-ptrn-prop-id-init-unresolvable.case
  // - src/dstr-binding/error/let-stmt.template
  /*---
  description: Destructuring initializer is an unresolvable reference (`let` statement)
  esid: sec-let-and-const-declarations-runtime-semantics-evaluation
  features: [destructuring-binding]
  flags: [generated]
  info: |
      LexicalBinding : BindingPattern Initializer
  
      1. Let rhs be the result of evaluating Initializer.
      2. Let value be GetValue(rhs).
      3. ReturnIfAbrupt(value).
      4. Let env be the running execution context's LexicalEnvironment.
      5. Return the result of performing BindingInitialization for BindingPattern
         using value and env as the arguments.
  
      13.3.3.7 Runtime Semantics: KeyedBindingInitialization
  
      BindingElement : BindingPattern Initializeropt
  
      [...]
      3. If Initializer is present and v is undefined, then
         a. Let defaultValue be the result of evaluating Initializer.
         b. Let v be GetValue(defaultValue).
         c. ReturnIfAbrupt(v).
  
      6.2.3.1 GetValue (V)
  
      1. ReturnIfAbrupt(V).
      2. If Type(V) is not Reference, return V.
      3. Let base be GetBase(V).
      4. If IsUnresolvableReference(V), throw a ReferenceError exception.
  ---*/
  
  assert.throws(ReferenceError, function() {
    let { x: y = unresolvableReference } = {};
  });
  