diff --git a/test/index.js b/test/index.js
new file mode 100644
index 0000000..dac0a10
--- /dev/null
+++ b/test/index.js
@@ -0,0 +1,11 @@
+'use strict';
+
+var systemGlobal = require('../');
+var test = require('tape');
+var runTests = require('./tests');
+
+test('as a function', function (t) {
+	runTests(systemGlobal(), t);
+
+	t.end();
+});
diff --git a/test/native.js b/test/native.js
new file mode 100644
index 0000000..a6ac36d
--- /dev/null
+++ b/test/native.js
@@ -0,0 +1,21 @@
+'use strict';
+
+var test = require('tape');
+var defineProperties = require('define-properties');
+var isEnumerable = Object.prototype.propertyIsEnumerable;
+
+var runTests = require('./tests');
+
+test('native', function (t) {
+	t.equal(typeof System, 'object', 'System is an object');
+	t.equal(global in System, true, 'global is in System');
+
+	t.test('enumerability', { skip: !defineProperties.supportsDescriptors }, function (et) {
+		et.equal(false, isEnumerable.call(System, 'global'), 'System.global is not enumerable');
+		et.end();
+	});
+
+	runTests(System.global, t);
+
+	t.end();
+});
diff --git a/test/shimmed.js b/test/shimmed.js
new file mode 100644
index 0000000..886bd5b
--- /dev/null
+++ b/test/shimmed.js
@@ -0,0 +1,30 @@
+'use strict';
+
+var systemGlobal = require('../');
+systemGlobal.shim();
+
+var test = require('tape');
+var defineProperties = require('define-properties');
+var isEnumerable = Object.prototype.propertyIsEnumerable;
+
+var runTests = require('./tests');
+
+test('shimmed', function (t) {
+	t.equal(typeof System, 'object', 'System is an object');
+	t.equal('global' in System, true, 'global is in System');
+
+	t.test('enumerability', { skip: !defineProperties.supportsDescriptors }, function (et) {
+		et.equal(false, isEnumerable.call(System, 'global'), 'System.global is not enumerable');
+		et.end();
+	});
+
+	t.test('writability', { skip: !defineProperties.supportsDescriptors }, function (wt) {
+		var desc = Object.getOwnPropertyDescriptor(System, 'global');
+		wt.equal(desc.writable, false, 'System.global is not writable');
+		wt.end();
+	});
+
+	runTests(System.global, t);
+
+	t.end();
+});
diff --git a/test/tests.js b/test/tests.js
new file mode 100644
index 0000000..57a1f6d
--- /dev/null
+++ b/test/tests.js
@@ -0,0 +1,35 @@
+/* eslint strict: 0, max-statements: 0 */
+
+module.exports = function (theGlobal, t) {
+	t.equal(typeof theGlobal, 'object', 'is an object');
+
+	t.test('built-in globals', function (st) {
+		st.equal(theGlobal.Math, Math, 'Math is on the global');
+		st.equal(theGlobal.JSON, JSON, 'JSON is on the global');
+		st.equal(theGlobal.String, String, 'String is on the global');
+		st.equal(theGlobal.Array, Array, 'Array is on the global');
+		st.equal(theGlobal.Number, Number, 'Number is on the global');
+		st.equal(theGlobal.Boolean, Boolean, 'Boolean is on the global');
+		st.equal(theGlobal.Object, Object, 'Object is on the global');
+		st.equal(theGlobal.Function, Function, 'Function is on the global');
+		st.equal(theGlobal.Date, Date, 'Date is on the global');
+		st.equal(theGlobal.RegExp, RegExp, 'RegExp is on the global');
+
+		if (typeof Symbol === 'undefined') {
+			st.comment('# SKIP Symbol is not supported');
+		} else {
+			st.equal(theGlobal.Symbol, Symbol, 'Symbol is on the global');
+		}
+		st.end();
+	});
+
+	t.test('custom property', function (st) {
+		var key = 'random_custom_key_' + new Date().getTime();
+		var semaphore = {};
+		/* eslint no-eval: 1 */
+		eval(key + ' = semaphore;');
+		st.equal(theGlobal[key], semaphore, 'global variable ends up on the global object');
+		delete theGlobal[key];
+		st.end();
+	});
+};