Introduce Jest Unit Testing framework

test/client/setupJest.js

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+import Enzyme from 'enzyme';
+import Adapter from 'enzyme-adapter-react-15';
+
+Enzyme.configure({adapter: new Adapter()});
+
+// Storage Mock
+
+// TODO: If our code is written well, there shouldn't be a hardcoded dependency
+// to the local storage, and this global mock wouldn't be needed.
+
+function storageMock() {
+  let storage = {};
+
+  return {
+    setItem: function(key, value) {
+      storage[key] = value || '';
+    },
+    getItem: function(key) {
+      return key in storage ? storage[key] : null;
+    },
+    removeItem: function(key) {
+      delete storage[key];
+    },
+    get length() {
+      return Object.keys(storage).length;
+    },
+    key: function(i) {
+      let keys = Object.keys(storage);
+      return keys[i] || null;
+    }
+  };
+}
+
+// mock the localStorage
+window.localStorage = storageMock();
+
+// mock the sessionStorage
+window.sessionStorage = storageMock();