fix: max backoff should be 32 seconds (#792)

Author: olavloite

handwritten/spanner/src/transaction-runner.ts

@@ -152,7 +152,11 @@ export abstract class Runner<T> {
       return secondsInMs + nanosInMs;
     }
 
-    return Math.pow(2, this.attempts) * 1000 + Math.floor(Math.random() * 1000);
+    // Max backoff should be 32 seconds.
+    return (
+      Math.pow(2, Math.min(this.attempts, 5)) * 1000 +
+      Math.floor(Math.random() * 1000)
+    );
   }
   /**
    * Retrieves a transaction to run against.

handwritten/spanner/test/transaction-runner.ts

@@ -163,7 +163,22 @@ describe('TransactionRunner', () => {
       it('should create a backoff when `retryInfo` is absent', () => {
         const random = Math.random();
 
-        runner.attempts = 5;
+        runner.attempts = 3;
+        sandbox.stub(global.Math, 'random').returns(random);
+
+        const badError = new Error('err') as ServiceError;
+        badError.metadata = new Metadata();
+
+        const expectedDelay = Math.pow(2, 3) * 1000 + Math.floor(random * 1000);
+        const delay = runner.getNextDelay(badError);
+
+        assert.strictEqual(delay, expectedDelay);
+      });
+
+      it('should use a backoff of max 32 seconds when `retryInfo` is absent', () => {
+        const random = Math.random();
+
+        runner.attempts = 10;
         sandbox.stub(global.Math, 'random').returns(random);
 
         const badError = new Error('err') as ServiceError;