Maintainer feedback: Spec helper tests

* Adds test to cover `set_window_location_helper`

spec/frontend/helpers/set_window_location_helper_spec.js

+import setWindowLocationHelper from './set_window_location_helper';
+
+describe('setWindowLocationHelper', () => {
+  const originalLocation = window.location;
+
+  afterEach(() => {
+    window.location = originalLocation;
+  });
+
+  it.each`
+    locationProperty | value
+    ${'hash'}        | ${'foo'}
+    ${'host'}        | ${'gitlab.com'}
+    ${'hostname'}    | ${'gitlab.com'}
+    ${'href'}        | ${'https://gitlab.com/foo'}
+    ${'origin'}      | ${'https://gitlab.com'}
+    ${'origin'}      | ${'/foo'}
+    ${'port'}        | ${'80'}
+    ${'protocol'}    | ${'https:'}
+  `('sets "window.location.$locationProperty" to be $value', ({ locationProperty, value }) => {
+    expect(window.location[locationProperty]).not.toBe(value);
+
+    setWindowLocationHelper({
+      [locationProperty]: value,
+    });
+
+    expect(window.location[locationProperty]).toBe(value);
+  });
+});