Add tests. Use exactOptionalPropertyTypes in tsconfig

test/exponential-backoff.test.ts

@@ -1,6 +1,6 @@
 import { expect, test, vi } from 'vitest';
 import { ExponentialBackoff } from '../source/exponential-backoff.ts';
-import { ExponentialBackoffMaxRetriesHitError, ExponentialBackoffStoppedRetriesError } from '../source/errors.ts';
+import { ExponentialBackoffMaxRetriesHitError, ExponentialBackoffNumberNotFiniteError, ExponentialBackoffStoppedRetriesError } from '../source/errors.ts';
 
 /**
  * A valid options object that satisfies {@link ExponentialBackoff.validateOptions}.
@@ -582,6 +582,39 @@ const testExponentialBackoffValidateOptionsRejectsNaN = (): void => {
     }
 };
 
+/** Tests that calculateDelay will not result in NaN from extremely large growth rates and attempts */
+const testExponentialBackoffCalculateDelayDoesNotResultInNaN = (): void => {
+    // Large number, 1 trillion.
+    // Theory being that 1 trillion to the power of 1 trillion should be a very large number and cause either an unsafe value or a NaN.
+    const largeNumber = 1_000_000_000_000;
+
+    // Test the calculateDelay function
+    const result = ExponentialBackoff.calculateDelay({
+        baseDelay: 10000,
+        growthRate: largeNumber,
+        jitter: 0,
+        maxDelay: 10_000,
+        maxAttempts: largeNumber,
+    }, largeNumber);
+
+    // Test to ensure it was bounded to the max delay
+    expect(result).toBe(10_000);
+};
+
+/** Tests that passing undefined into the constructor does not cause an error during spread */
+const testExponentialBackoffConstructorDoesNotCauseErrorDuringSpread = async (): Promise<void> => {
+    const options = {
+        baseDelay: undefined,
+        growthRate: undefined,
+        jitter: undefined,
+        maxDelay: undefined,
+        maxAttempts: undefined,
+    };
+
+    // We expect an error during validation as undefined is not a finite number, not an issue with the spread operator
+    // @ts-expect-error - Passing undefined is allowed if the exactOptionalPropertyTypes option is set to false in TS Compiler options.
+    expect(() => new ExponentialBackoff(options)).toThrow(ExponentialBackoffNumberNotFiniteError);
+};
 const runTests = async (): Promise<void> => {
     test('ExponentialBackoff.run: delegates to a new instance using default options', testExponentialBackoffRunUsesDefaultOptions);
     test('ExponentialBackoff.run: retries and succeeds with partial options', testExponentialBackoffRunWithPartialOptions);
@@ -608,6 +641,8 @@ const runTests = async (): Promise<void> => {
     test('ExponentialBackoff.validateOptions: rejects Infinity', testExponentialBackoffValidateOptionsRejectsNonFiniteValues);
     test('ExponentialBackoff.validateOptions: rejects non-integer values', testExponentialBackoffValidateOptionsRejectsNonIntegerValues);
     test('ExponentialBackoff.validateOptions: rejects NaN', testExponentialBackoffValidateOptionsRejectsNaN);
+    test('ExponentialBackoff: calculateDelay does not result in NaN from extremely large growth rates and attempts', testExponentialBackoffCalculateDelayDoesNotResultInNaN);
+    test('ExponentialBackoff: constructor does not cause an error during spread', testExponentialBackoffConstructorDoesNotCauseErrorDuringSpread);
 };
 
 await runTests();