# 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](https://tc39.github.io/ecma262/#sec-code-realms) dedicated to that test. Unless configured otherwise (via the `module` flag), source text must be interpreted as [global code](http://www.ecma-international.org/ecma-262/6.0/#sec-types-of-source-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). - **`$`** An ordinary object with the following properties: - **`createRealm`** - a function which creates a new [ECMAScript Realm](https://tc39.github.io/ecma262/2016/#sec-code-realms), defines this API on the new realm's global object, and returns the `$` property of the new realm's global object - **`detachArrayBuffer`** - a function which implements [the DetachArrayBuffer abstract operation](https://tc39.github.io/ecma262/2016/#sec-detacharraybuffer) - **`evalScript`** - a function which accepts a string value as its first argument and executes is as [an ECMAScript script](https://tc39.github.io/ecma262/2016/#sec-scripts) according to the following algorithm: 1. Let hostDefined be any host-defined values for the provided sourceText (obtained in an implementation dependent manner) 2. Let realm be the current Realm Record. 3. Let s be ParseScript(sourceText, realm, hostDefined). 4. If s is a List of errors, then a. Let error be the first element of s. b. Return Completion{[[Type]]: throw, [[Value]]: error, [[Target]]: empty}. 5. Let status be ScriptEvaluation(s). 6. Return Completion(status). - **`global`** - a reference to the global object on which `$` was initially defined ### 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](https://tc39.github.io/ecma262/#sec-directive-prologues-and-the-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. ### Modules Test262 includes tests for ECMAScript 2015 module code, denoted by the "module" metadata flag. Files bearing a name ending in `_FIXTURE.js` should not be interpreted as standalone tests; they are intended to be referenced by test files. All module specifiers used by Test262 begin with the character sequence `./`. The remaining characters should be interpreted as the name of a file within the same directory as the file under test. The contents of this file must be interpreted as UTF-8-encoded text and supplied to the Source Text Module Record's ParseModule abstract operation. The result of that operation must be returned by the implementation-defined HostResolveImportedModule directly. For example, consider a test file located at `test/language/import/nested/index.js` with the following contents: ```js import * as ns from './dep.js'; ``` Implementers should attempt to resolve this module specifier by loading a file located at `test/language/import/nested/dep.js`. ## 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](http://yaml.org/). ### `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:* ```js /*--- 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* ```js /*--- 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* ```js /*--- 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* ```js /*--- 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](http://www.ecma-international.org/ecma-262/6.0/#sec-types-of-source-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. Refer to the section titled "Modules" for more information on interpreting these tests. *Example* ```js /*--- 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* ```js /*--- 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* ```js /*--- flags: [async] ---*/ Promise.resolve() .then(function() { print('Test262:AsyncTestComplete'); }, function(reason) { print('Error: ' + reason); }); ```