Ensured that tests are not run without the minimum required node version

docs/DEV.md

@@ -98,8 +98,6 @@ Code at [/test/functional_tests.js](/test/functional_tests.js).
 
 Note: The study variation/branch during tests is overridden by a preference in the FIREFOX_PREFERENCES section of `test/utils.js`.
 
-(The functional tests are using async/await, so make sure you are running Node 7.6+)
-
 The functional testing set-up is a minimal set of tests imported from <https://github.com/mozilla/share-button-study> which contains plenty of examples of functional tests relevant to Shield study addons.
 
 ## Directory Structure and Files

package.json

@@ -60,6 +60,7 @@
     "lint:web-ext-lint": "WEB_EXT_VERBOSE=false web-ext lint",
     "postformat": "npm run eslint-fix",
     "prebuild": "npm run bundle-utils",
+    "pretest": "node test/ensure_minimum_node_version.js",
     "prewatch": "npm run bundle-utils",
     "sign": "echo 'TBD, see: https://bugzilla.mozilla.org/show_bug.cgi?id=1407757'",
     "start": "web-ext run --no-reload",

test/ensure_minimum_node_version.js

@@ -0,0 +1,11 @@
+/* eslint-env node */
+
+const semver = require("semver");
+const requiredNodeEngineVersion = require("../package.json").engines.node;
+const currentNodeEngineVersion = process.versions.node;
+if (!semver.satisfies(currentNodeEngineVersion, requiredNodeEngineVersion)) {
+  console.error(
+    `Node version needs to be ${requiredNodeEngineVersion} for tests to run. Currently ${currentNodeEngineVersion}. Exiting...`,
+  );
+  process.exit(1);
+}