test262/INTERPRETING.md

Interpreting Test262 Tests

All tests are declared as text files located within this project's test directory. In order to execute Test262 tests, runtimes must observe the following semantics.

Test Execution

Test262 tests are only valid under the runtime environment conditions described here. Test environments may be further modified according to the metadata contained with each test--refer to the "Metadata" section for more details.

Realm Isolation

Each test must be executed in a new ECMAScript realm dedicated to that test. Unless configured otherwise (via the module flag), source text must be interpreted as global code.

Test262-Defined Bindings

The contents of the following files must be evaluated in the test realm's global scope prior to test execution:

1. harness/assert.js
2. harness/sta.js

Host-Defined Functions

The following values must be defined as writable, configurable, non-enumerable properties of the global scope prior to test execution.

• print A function that exposes the string value of its first argument to the test runner. This is used as a communication mechanism for asynchronous tests (via the async flag, described below).

Strict Mode

Unless configured otherwise (via the noStrict, onlyStrict, module, or raw flags), each test must be executed twice: once in ECMAScript's non-strict mode, and again in ECMAScript's strict mode. To run in strict mode, the test contents must be modified prior to execution--a "use strict" directive must be inserted as the initial character sequence of the file, followed by a semicolon (;) and newline character (\n):

"use strict";

This must precede any additional text modifications described by test metadata.

Test Results

By default, tests signal failure by generating an uncaught exception. If execution completes without generating an exception, the test must be interpreted as "passing." Any uncaught exception must be interpreted as test failure. These semantics may be modified by any test according to the metadata declared within the test itself (via the negative attribute and the async flag, described below).

Metadata

Each test file may define metadata that describe additional requirements. This information is delimited by the token sequence /*--- and ---*/ and is structured as YAML.

negative

These tests are expected to generate an uncaught exception. The value of this attribute is the name of the constructor of the expected error. If a test configured with the negative attribute completes without throwing an exception, or if the name of the thrown exception's constructor does not match the specified constructor name, the test must be interpreted as "failing."

Example:

/*---
negative: ReferenceError
---*/
unresolvable;

includes

One or more files whose content must be evaluated in the test realm's global scope prior to test execution. These files are located within the harness/ directory of the Test262 project.

Example

/*---
includes: [testBuildInObject.js]
---*/
testBuiltInObject(Number.prototype.toLocaleString, true, false, [], 0);

flags

The flags attribute is an optional value that specifies one or more of the following strings:

• onlyStrict The test must be executed just once--in strict mode, only. This must be accomplished using the transformation described in the section titled "Strict Mode".

  Example

  /*---
  flags: [onlyStrict]
  ---*/
  var thisVal = null;
  [null].forEach(function() {
    thisVal = this;
  });
  assert.sameValue(thisVal, undefined);
  

• noStrict The test must be executed just once--in non-strict mode, only. In other words, the transformation described by the section titled "Strict Mode" must not be applied to these tests.

  Example

  /*---
  flags: [noStrict]
  ---*/
  var thisVal = null;
  [null].forEach(function() {
    thisVal = this;
  });
  assert.notSameValue(thisVal, undefined);
  assert.sameValue(thisVal, this);
  

• module The test source code must be interpreted as module code. In addition, this flag negates the default requirement to execute the test both in strict mode and in non-strict mode. In other words, the transformation described by the section titled "Strict Mode" must not be applied to these tests.

  Example

  /*---
  flags: [module]
  ---*/
  export default function* g() {}
  

• raw The test source code must not be modified in any way, and the test must be executed just once (in non-strict mode, only).

  Example

  /*---
  flags: [raw]
  ---*/
  'use strict'
  [0]
  's'.p = null;
  

• async The file harness/donePrintHandle.js must be evaluated in the test realm's global scope prior to test execution. The test must not be considered complete until the implementation-defined print function has been invoked or some length of time has passed without any such invocation. In the event of a passing test run, this function will be invoked with the string 'Test262:AsyncTestComplete'. If invoked with any other value, the test must be interpreted as failed. The implementation is free to select an appropriate length of time to wait before considering the test "timed out" and failing.

  Example

  /*---
  flags: [async]
  ---*/
  Promise.resolve()
    .then(function() {
        print('Test262:AsyncTestComplete');
      }, function(reason) {
        print('Error: ' + reason);
      });