1 files changed, 77 insertions, 0 deletions
diff --git a/spec/frontend/lib/utils/sticky_spec.js b/spec/frontend/lib/utils/sticky_spec.js
new file mode 100644
index 00000000000..4ad68cc9ff6
--- /dev/null
+++ b/spec/frontend/lib/utils/sticky_spec.js
@@ -0,0 +1,77 @@
+import { isSticky } from '~/lib/utils/sticky';
+import { setHTMLFixture } from 'helpers/fixtures';
+
+const TEST_OFFSET_TOP = 500;
+
+describe('sticky', () => {
+  let el;
+  let offsetTop;
+
+  beforeEach(() => {
+    setHTMLFixture(
+      `
+      <div class="parent">
+        <div id="js-sticky"></div>
+      </div>
+    `,
+    );
+
+    offsetTop = TEST_OFFSET_TOP;
+    el = document.getElementById('js-sticky');
+    Object.defineProperty(el, 'offsetTop', {
+      get() {
+        return offsetTop;
+      },
+    });
+  });
+
+  afterEach(() => {
+    el = null;
+  });
+
+  describe('when stuck', () => {
+    it('does not remove is-stuck class', () => {
+      isSticky(el, 0, el.offsetTop);
+      isSticky(el, 0, el.offsetTop);
+
+      expect(el.classList.contains('is-stuck')).toBeTruthy();
+    });
+
+    it('adds is-stuck class', () => {
+      isSticky(el, 0, el.offsetTop);
+
+      expect(el.classList.contains('is-stuck')).toBeTruthy();
+    });
+
+    it('inserts placeholder element', () => {
+      isSticky(el, 0, el.offsetTop, true);
+
+      expect(document.querySelector('.sticky-placeholder')).not.toBeNull();
+    });
+  });
+
+  describe('when not stuck', () => {
+    it('removes is-stuck class', () => {
+      jest.spyOn(el.classList, 'remove');
+
+      isSticky(el, 0, el.offsetTop);
+      isSticky(el, 0, 0);
+
+      expect(el.classList.remove).toHaveBeenCalledWith('is-stuck');
+      expect(el.classList.contains('is-stuck')).toBe(false);
+    });
+
+    it('does not add is-stuck class', () => {
+      isSticky(el, 0, 0);
+
+      expect(el.classList.contains('is-stuck')).toBeFalsy();
+    });
+
+    it('removes placeholder', () => {
+      isSticky(el, 0, el.offsetTop, true);
+      isSticky(el, 0, 0, true);
+
+      expect(document.querySelector('.sticky-placeholder')).toBeNull();
+    });
+  });
+});