Run tests in JSDOM env with force GC

  JSDOM is default environment in Jest

  Here we only extend this environment to be able to start
  V8 garbadge collection at the end of each suite testing

  This allows to show clearer picture of heap usage by each test suite
  as GC now runs exactly between test suites (before it had some lazy
  behaviour about when to run GC)

Author: FreeleX

jest-jsdom-env.js

@@ -0,0 +1,20 @@
+const vm = require('vm');
+const v8 = require('v8');
+
+const JSDomEnvironment = require('jest-environment-jsdom');
+
+class JSDomEnvironmentWithForceGC extends JSDomEnvironment {
+    teardown() {
+        return super.teardown().then(() => {
+            const isGlobaGCHidden = !global.gc;
+
+            v8.setFlagsFromString('--expose-gc');
+            vm.runInNewContext('gc')();
+            if (isGlobaGCHidden) {
+                v8.setFlagsFromString('--no-expose-gc');
+            }
+        });
+    }
+}
+
+module.exports = JSDomEnvironmentWithForceGC;

jest.config.js

@@ -1,3 +1,4 @@
 module.exports = {
     setupTestFrameworkScriptFile: require.resolve('./setupJest'),
+    testEnvironment: require.resolve('./jest-jsdom-env'),
 };