1 files changed, 69 insertions, 0 deletions
diff --git a/spec/frontend/streaming/render_balancer_spec.js b/spec/frontend/streaming/render_balancer_spec.js
new file mode 100644
index 00000000000..dae0c98d678
--- /dev/null
+++ b/spec/frontend/streaming/render_balancer_spec.js
@@ -0,0 +1,69 @@
+import { RenderBalancer } from '~/streaming/render_balancer';
+
+const HIGH_FRAME_TIME = 100;
+const LOW_FRAME_TIME = 10;
+
+describe('renderBalancer', () => {
+  let frameTime = 0;
+  let frameTimeDelta = 0;
+  let decrease;
+  let increase;
+
+  const createBalancer = () => {
+    decrease = jest.fn();
+    increase = jest.fn();
+    return new RenderBalancer({
+      highFrameTime: HIGH_FRAME_TIME,
+      lowFrameTime: LOW_FRAME_TIME,
+      increase,
+      decrease,
+    });
+  };
+
+  const renderTimes = (times) => {
+    const balancer = createBalancer();
+    return new Promise((resolve) => {
+      let counter = 0;
+      balancer.render(() => {
+        if (counter === times) {
+          resolve(counter);
+          return false;
+        }
+        counter += 1;
+        return true;
+      });
+    });
+  };
+
+  beforeEach(() => {
+    jest.spyOn(window, 'requestAnimationFrame').mockImplementation((cb) => {
+      frameTime += frameTimeDelta;
+      cb(frameTime);
+    });
+  });
+
+  afterEach(() => {
+    window.requestAnimationFrame.mockRestore();
+    frameTime = 0;
+    frameTimeDelta = 0;
+  });
+
+  it('renders in a loop', async () => {
+    const count = await renderTimes(5);
+    expect(count).toBe(5);
+  });
+
+  it('calls decrease', async () => {
+    frameTimeDelta = 200;
+    await renderTimes(5);
+    expect(decrease).toHaveBeenCalled();
+    expect(increase).not.toHaveBeenCalled();
+  });
+
+  it('calls increase', async () => {
+    frameTimeDelta = 1;
+    await renderTimes(5);
+    expect(increase).toHaveBeenCalled();
+    expect(decrease).not.toHaveBeenCalled();
+  });
+});