Ensure module and test callbacks are released for GC.

build/tasks/test-on-node.js

@@ -36,6 +36,9 @@ module.exports = function( grunt ) {
 			grunt.log.writeln( "-----" );
 			grunt.log.ok( constructMessage( totals ) );
 
+			// Refresh the QUnit global to be used in other tests
+			global.QUnit = requireFresh( "../../dist/qunit" );
+
 			done( !error );
 		} );
 	} );

src/test.js

@@ -254,6 +254,10 @@ Test.prototype = {
 	finish: function() {
 		config.current = this;
 
+		// Release the test callback to ensure that anything referenced has been
+		// released to be garbage collected.
+		this.callback = undefined;
+
 		if ( this.steps.length ) {
 			const stepsList = this.steps.join( ", " );
 			this.pushFailure( "Expected assert.verifySteps() to be called before end of test " +
@@ -342,6 +346,11 @@ Test.prototype = {
 		config.current = undefined;
 
 		function logSuiteEnd( module ) {
+
+			// Reset `module.hooks` to ensure that anything referenced in these hooks
+			// has been released to be garbage collected.
+			module.hooks = {};
+
 			emit( "suiteEnd", module.suiteReport.end( true ) );
 			runLoggingCallbacks( "moduleDone", {
 				name: module.name,
@@ -351,6 +360,7 @@ Test.prototype = {
 				total: module.stats.all,
 				runtime: now() - module.stats.started
 			} );
+
 		}
 	},
 

test/cli/fixtures/expected/tap-outputs.js

@@ -169,5 +169,15 @@ ok 1 Single > has a test
 # pass 1
 # skip 0
 # todo 0
+# fail 0`,
+
+	"node --expose-gc --allow-natives-syntax ../../../bin/qunit memory-leak/*.js":
+`TAP version 13
+ok 1 some nested module > can call method on foo
+ok 2 later thing > has released all foos
+1..2
+# pass 2
+# skip 0
+# todo 0
 # fail 0`
 };

test/cli/fixtures/memory-leak/index.js

@@ -0,0 +1,60 @@
+/* globals gc */
+
+const foos = new WeakSet();
+class Foo {
+	constructor() {
+		foos.add( this );
+	}
+
+	sayHello() {
+		return "Hi!";
+	}
+
+	destroy() { }
+}
+
+QUnit.module( "some nested module", function( hooks ) {
+	let foo;
+
+	hooks.beforeEach( function() {
+		foo = new Foo();
+	} );
+
+	hooks.afterEach( function() {
+		foo.destroy();
+	} );
+
+	QUnit.test( "can call method on foo", function( assert ) {
+		assert.equal( foo.sayHello(), "Hi!" );
+	} );
+
+} );
+
+QUnit.module( "later thing", function() {
+	QUnit.test( "has released all foos", function( assert ) {
+
+		// Without async here, the test runner is recursive, and therefore the `foo`
+		// instance is still retained.
+		return Promise.resolve()
+			.then( () => {
+
+				// Requires `--expose-gc` flag to function properly.
+				gc();
+
+				// Using `new Function` here to avoid a syntax error.
+				const retainedFoos = new Function(
+					"foos",
+					"return %GetWeakSetValues(foos, 0)"
+				)( foos );
+
+				assert.equal( retainedFoos.length, 0 );
+			} )
+			.catch( error => {
+				if ( error instanceof SyntaxError ) {
+					console.log( "Must launch Node 9 with `--expose-gc --allow-natives-syntax`" );
+				} else {
+					throw error;
+				}
+			} );
+	} );
+} );

test/cli/main.js

@@ -4,6 +4,7 @@ const co = require( "co" );
 
 const expectedOutput = require( "./fixtures/expected/tap-outputs" );
 const execute = require( "./helpers/execute" );
+const semver = require( "semver" );
 
 QUnit.module( "CLI Main", function() {
 	QUnit.test( "defaults to running tests in 'test' directory", co.wrap( function* ( assert ) {
@@ -123,6 +124,17 @@ QUnit.module( "CLI Main", function() {
 		}
 	} ) );
 
+	if ( semver.gte( process.versions.node, "9.0.0" ) ) {
+		QUnit.test( "callbacks and hooks from modules are properly released for garbage collection", co.wrap( function* ( assert ) {
+			const command = "node --expose-gc --allow-natives-syntax ../../../bin/qunit memory-leak/*.js";
+			const execution = yield execute( command );
+
+			assert.equal( execution.code, 0 );
+			assert.equal( execution.stderr, "" );
+			assert.equal( execution.stdout, expectedOutput[ command ] );
+		} ) );
+	}
+
 	QUnit.module( "filter", function() {
 		QUnit.test( "can properly filter tests", co.wrap( function* ( assert ) {
 			const command = "qunit --filter 'single' test single.js 'glob/**/*-test.js'";