Add a test to ensure the library can be imported

Author: alexlafroscia

tests/unit/testdouble-import-test.js

@@ -0,0 +1,11 @@
+import { module, test } from 'qunit';
+import td from 'testdouble';
+
+module('testdouble import');
+
+test('can import `testdouble`', function(assert) {
+  const double = td.function();
+  td.when(double('foo')).thenReturn('bar');
+
+  assert.equal(double('foo'), 'bar');
+});