Add test for abort during exponential backoff waiting period

tests/utils/exponential-backoff.test.ts

@@ -261,6 +261,46 @@ const testExponentialBackoffRunWithAbortSignal = async (): Promise<void> => {
     expect(abortAndThrowFn).not.toHaveResolved();
 };
 
+/**
+ * Tests that aborting while the delay between attempts is active rejects the
+ * pending wait immediately and prevents the next attempt from starting.
+ */
+const testExponentialBackoffAbortsDuringDelay = async (): Promise<void> => {
+    vi.useFakeTimers();
+
+    try {
+        let abortRetry: ((reason?: unknown) => void) | undefined;
+        const rejectedFn = vi.fn(async ({ abort }) => {
+            abortRetry = abort;
+
+            throw new Error('attempt failed');
+        });
+        const onError = vi.fn();
+
+        const result = ExponentialBackoff.run(rejectedFn, onError, {
+            baseDelay: 1_000,
+            maxDelay: 1_000,
+            maxAttempts: 2,
+            growthRate: 1,
+            jitter: 0,
+        });
+
+        // Run the first attempt, enter the retry delay, then stop halfway through it.
+        await vi.advanceTimersByTimeAsync(500);
+        expect(abortRetry).toBeDefined();
+        expect(vi.getTimerCount()).toBe(1);
+
+        abortRetry?.(new Error('cancelled during delay'));
+
+        await expect(result).rejects.toThrow('Exponential backoff aborted');
+        expect(rejectedFn).toHaveBeenCalledOnce();
+        expect(onError).toHaveBeenCalledOnce();
+        expect(vi.getTimerCount()).toBe(0);
+    } finally {
+        vi.useRealTimers();
+    }
+};
+
 /**
  * Tests that when the abort signal is aborted with a string, an AggregateError is thrown
  * with the string as the message.
@@ -578,6 +618,7 @@ const runTests = async (): Promise<void> => {
     test('ExponentialBackoff: wraps non-Error throws before calling onError', testExponentialBackoffWrapsNonErrorThrows);
     test('ExponentialBackoff: succeeds and aborts with abort signal', testExponentialBackoffRunSuccessAndAbortSignal);
     test('ExponentialBackoff: aborts with abort signal', testExponentialBackoffRunWithAbortSignal);
+    test('ExponentialBackoff: aborts while waiting between attempts', testExponentialBackoffAbortsDuringDelay);
     test('ExponentialBackoff: aborts with aborted string creates error', testExponentialBackoffRunAbortedStringCreatesError);
     test('ExponentialBackoff: works via from and instance run', testExponentialBackoffFromAndInstanceRun);
     test('ExponentialBackoff: retries indefinitely when maxAttempts is 0', testExponentialBackoffRetriesIndefinitelyWhenMaxAttemptsIsZero);