get rid of App and add test for ProcessBreadcrumb component

src/App.js

@@ -1,25 +0,0 @@
-import "bpmn-js/dist/assets/diagram-js.css";
-import "bpmn-js/dist/assets/bpmn-font/css/bpmn-embedded.css";
-// import ReactBpmnEditor from "./react_bpmn_editor"
-import { Link } from "react-router-dom";
-import ProcessGroups from "./routes/ProcessGroups"
-
-
-function App() {
-  function onError(err) {
-    console.log('ERROR:', err);
-  }
-
-    // <ReactBpmnEditor
-    // url={process.env.PUBLIC_URL + '/sample.bpmn'}
-    // onError={ onError }
-    // />
-    // <Link to="/expenses">Expenses</Link>
-  return (
-    <div>
-    <Link to="/process-groups">Process Groups</Link>
-    </div>
-  );
-}
-
-export default App;

src/App.test.js

@@ -1,8 +0,0 @@
-import { render, screen } from '@testing-library/react';
-import App from './App';
-
-test('renders learn react link', () => {
-  render(<App />);
-  const linkElement = screen.getByText(/learn react/i);
-  expect(linkElement).toBeInTheDocument();
-});

src/components/ProcessBreadcrumb.test.js

@@ -0,0 +1,31 @@
+import { render, screen } from '@testing-library/react';
+import ProcessBreadcrumb from './ProcessBreadcrumb';
+import {
+  BrowserRouter,
+} from "react-router-dom";
+
+test('renders home link', () => {
+  render(<BrowserRouter><ProcessBreadcrumb /></BrowserRouter>);
+  const homeElement = screen.getByText(/Home/);
+  expect(homeElement).toBeInTheDocument();
+});
+
+test('renders process group link when processGroupId', () => {
+  const { container } = render(<BrowserRouter><ProcessBreadcrumb processGroupId='group-a'/></BrowserRouter>);
+  const processGroupElement = screen.getByText(/group-a/);
+  expect(processGroupElement).toBeInTheDocument();
+  const activeBreadcrumbElements = container.getElementsByClassName('breadcrumb-item active')
+  expect(activeBreadcrumbElements.length).toBe(1);
+  expect(activeBreadcrumbElements[0].innerHTML).toEqual("Process Group: group-a");
+});
+
+test('renders processmodelgroup link when processModelId', () => {
+  const { container } = render(<BrowserRouter><ProcessBreadcrumb processGroupId='group-b' processModelId='model-c'/></BrowserRouter>);
+  const processGroupElement = screen.getByText(/group-b/);
+  expect(processGroupElement).toBeInTheDocument();
+  const activeBreadcrumbElements = container.getElementsByClassName('breadcrumb-item active')
+  expect(activeBreadcrumbElements.length).toBe(1);
+  expect(activeBreadcrumbElements[0].innerHTML).toEqual("Process Model: model-c");
+  const processModelElement = screen.getByText(/model-c/);
+  expect(processModelElement).toBeInTheDocument();
+});