add testability tests

specs/Modal.testability.spec.js

@@ -0,0 +1,23 @@
+import ReactDOM from "react-dom";
+import sinon from "sinon";
+import {
+  mcontent,
+  renderModal,
+  emptyDOM
+} from "./helper";
+
+export default () => {
+  afterEach("cleaned up all rendered modals", emptyDOM);
+
+  it("renders as expected, initially", () => {
+    const modal = renderModal({ isOpen: true }, "hello");
+    mcontent(modal).should.be.ok();
+  });
+
+  it("allows ReactDOM.createPortal to be overridden in real-time", () => {
+    const createPortalSpy = sinon.spy(ReactDOM, "createPortal");
+    renderModal({ isOpen: true }, "hello");
+    createPortalSpy.called.should.be.ok();
+    ReactDOM.createPortal.restore();
+  });
+};

specs/index.js

@@ -4,8 +4,10 @@ import ModalState from "./Modal.spec";
 import ModalEvents from "./Modal.events.spec";
 import ModalStyle from "./Modal.style.spec";
 import ModalHelpers from "./Modal.helpers.spec";
+import ModalTestability from "./Modal.testability.spec";
 
 describe("State", ModalState);
 describe("Style", ModalStyle);
 describe("Events", ModalEvents);
 describe("Helpers", ModalHelpers);
+describe("Testability", ModalTestability);