1 files changed, 79 insertions, 0 deletions
diff --git a/spec/javascripts/lib/utils/sticky_spec.js b/spec/javascripts/lib/utils/sticky_spec.js
new file mode 100644
index 00000000000..b87c836654d
--- /dev/null
+++ b/spec/javascripts/lib/utils/sticky_spec.js
@@ -0,0 +1,79 @@
+import { isSticky } from '~/lib/utils/sticky';
+
+describe('sticky', () => {
+  let el;
+
+  beforeEach(() => {
+    document.body.innerHTML += `
+      <div class="parent">
+        <div id="js-sticky"></div>
+      </div>
+    `;
+
+    el = document.getElementById('js-sticky');
+  });
+
+  afterEach(() => {
+    el.parentNode.remove();
+  });
+
+  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', () => {
+      spyOn(el.classList, 'remove').and.callThrough();
+
+      isSticky(el, 0, el.offsetTop);
+      isSticky(el, 0, 0);
+
+      expect(
+        el.classList.remove,
+      ).toHaveBeenCalledWith('is-stuck');
+      expect(
+        el.classList.contains('is-stuck'),
+      ).toBeFalsy();
+    });
+
+    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();
+    });
+  });
+});