1 files changed, 49 insertions, 0 deletions
diff --git a/spec/frontend/__helpers__/local_storage_helper.js b/spec/frontend/__helpers__/local_storage_helper.js
new file mode 100644
index 00000000000..21749fd8070
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+++ b/spec/frontend/__helpers__/local_storage_helper.js
@@ -0,0 +1,49 @@
+/**
+ * Manage the instance of a custom `window.localStorage`
+ *
+ * This only encapsulates the setup / teardown logic so that it can easily be
+ * reused with different implementations (i.e. a spy or a [fake][1])
+ *
+ * [1]: https://stackoverflow.com/a/41434763/1708147
+ *
+ * @param {() => any} fn Function that returns the object to use for localStorage
+ */
+const useLocalStorage = (fn) => {
+  const origLocalStorage = window.localStorage;
+  let currentLocalStorage = origLocalStorage;
+
+  Object.defineProperty(window, 'localStorage', {
+    get: () => currentLocalStorage,
+  });
+
+  beforeEach(() => {
+    currentLocalStorage = fn();
+  });
+
+  afterEach(() => {
+    currentLocalStorage = origLocalStorage;
+  });
+};
+
+/**
+ * Create an object with the localStorage interface but `jest.fn()` implementations.
+ */
+export const createLocalStorageSpy = () => {
+  let storage = {};
+
+  return {
+    clear: jest.fn(() => {
+      storage = {};
+    }),
+    getItem: jest.fn((key) => (key in storage ? storage[key] : null)),
+    setItem: jest.fn((key, value) => {
+      storage[key] = value;
+    }),
+    removeItem: jest.fn((key) => delete storage[key]),
+  };
+};
+
+/**
+ * Before each test, overwrite `window.localStorage` with a spy implementation.
+ */
+export const useLocalStorageSpy = () => useLocalStorage(createLocalStorageSpy);