Add tether service

app/tests/unit/services/tether-test.js

@@ -0,0 +1,12 @@
+import { moduleFor, test } from 'ember-qunit';
+
+moduleFor('service:tether', 'Unit | Service | tether', {
+  // Specify the other units that are required for this test.
+  // needs: ['service:foo']
+});
+
+// Replace this with your real tests.
+test('it exists', function(assert) {
+  let service = this.subject();
+  assert.ok(service);
+});