Add jest snapshot testing

lms/djangoapps/instructor/static/instructor/ProblemBrowser/components/Main/Main.test.jsx

@@ -0,0 +1,9 @@
+import React from 'react';
+import Main from './Main.jsx';
+import renderer from 'react-test-renderer';
+
+test('My first demo test', () => {
+  const component = renderer.create(<Main></Main>);
+  let tree = component.toJSON();
+  expect(tree).toMatchSnapshot();
+});

lms/djangoapps/instructor/static/instructor/ProblemBrowser/components/Main/__snapshots__/Main.test.jsx.snap

@@ -0,0 +1,22 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`My first demo test 1`] = `
+<div
+  className="problem-browser"
+>
+  <button
+    className="btn"
+    onBlur={[Function]}
+    onClick={[Function]}
+    onKeyDown={[Function]}
+    type="button"
+  >
+    Select a section or problem
+  </button>
+  <input
+    disabled={true}
+    name="problem-location"
+    type="text"
+  />
+</div>
+`;