1 files changed, 79 insertions, 0 deletions
diff --git a/spec/frontend/actioncable_connection_monitor_spec.js b/spec/frontend/actioncable_connection_monitor_spec.js
new file mode 100644
index 00000000000..c68eb53acde
--- /dev/null
+++ b/spec/frontend/actioncable_connection_monitor_spec.js
@@ -0,0 +1,79 @@
+import ConnectionMonitor from '~/actioncable_connection_monitor';
+
+describe('ConnectionMonitor', () => {
+  let monitor;
+
+  beforeEach(() => {
+    monitor = new ConnectionMonitor({});
+  });
+
+  describe('#getPollInterval', () => {
+    beforeEach(() => {
+      Math.originalRandom = Math.random;
+    });
+    afterEach(() => {
+      Math.random = Math.originalRandom;
+    });
+
+    const { staleThreshold, reconnectionBackoffRate } = ConnectionMonitor;
+    const backoffFactor = 1 + reconnectionBackoffRate;
+    const ms = 1000;
+
+    it('uses exponential backoff', () => {
+      Math.random = () => 0;
+
+      monitor.reconnectAttempts = 0;
+      expect(monitor.getPollInterval()).toEqual(staleThreshold * ms);
+
+      monitor.reconnectAttempts = 1;
+      expect(monitor.getPollInterval()).toEqual(staleThreshold * backoffFactor * ms);
+
+      monitor.reconnectAttempts = 2;
+      expect(monitor.getPollInterval()).toEqual(
+        staleThreshold * backoffFactor * backoffFactor * ms,
+      );
+    });
+
+    it('caps exponential backoff after some number of reconnection attempts', () => {
+      Math.random = () => 0;
+      monitor.reconnectAttempts = 42;
+      const cappedPollInterval = monitor.getPollInterval();
+
+      monitor.reconnectAttempts = 9001;
+      expect(monitor.getPollInterval()).toEqual(cappedPollInterval);
+    });
+
+    it('uses 100% jitter when 0 reconnection attempts', () => {
+      Math.random = () => 0;
+      expect(monitor.getPollInterval()).toEqual(staleThreshold * ms);
+
+      Math.random = () => 0.5;
+      expect(monitor.getPollInterval()).toEqual(staleThreshold * 1.5 * ms);
+    });
+
+    it('uses reconnectionBackoffRate for jitter when >0 reconnection attempts', () => {
+      monitor.reconnectAttempts = 1;
+
+      Math.random = () => 0.25;
+      expect(monitor.getPollInterval()).toEqual(
+        staleThreshold * backoffFactor * (1 + reconnectionBackoffRate * 0.25) * ms,
+      );
+
+      Math.random = () => 0.5;
+      expect(monitor.getPollInterval()).toEqual(
+        staleThreshold * backoffFactor * (1 + reconnectionBackoffRate * 0.5) * ms,
+      );
+    });
+
+    it('applies jitter after capped exponential backoff', () => {
+      monitor.reconnectAttempts = 9001;
+
+      Math.random = () => 0;
+      const withoutJitter = monitor.getPollInterval();
+      Math.random = () => 0.5;
+      const withJitter = monitor.getPollInterval();
+
+      expect(withJitter).toBeGreaterThan(withoutJitter);
+    });
+  });
+});