/**
* Unit tests for CircuitBreakerService
*
* Tests circuit breaker behavior:
* - Initial state
* - Successful execution
* - State transitions on failures
* - State queries
*/
import { CircuitBreakerService } from '../../../src/infrastructure/resilience/CircuitBreakerService.js';
describe('CircuitBreakerService', () => {
let stderrSpy: jest.SpyInstance;
beforeEach(() => {
// Suppress stderr output during tests
stderrSpy = jest.spyOn(process.stderr, 'write').mockImplementation(() => true);
});
afterEach(() => {
stderrSpy.mockRestore();
});
describe('initial state', () => {
it('starts in closed state', () => {
const cb = new CircuitBreakerService('test');
expect(cb.getState()).toBe('closed');
});
it('returns isOpen() as false initially', () => {
const cb = new CircuitBreakerService('test');
expect(cb.isOpen()).toBe(false);
});
});
describe('execute()', () => {
it('executes successfully when closed', async () => {
const cb = new CircuitBreakerService('test');
const result = await cb.execute(async () => 'success');
expect(result).toBe('success');
});
it('returns async operation result', async () => {
const cb = new CircuitBreakerService('test');
const result = await cb.execute(async () => {
return { data: 42 };
});
expect(result).toEqual({ data: 42 });
});
it('throws error on operation failure', async () => {
const cb = new CircuitBreakerService('test');
await expect(
cb.execute(async () => {
throw new Error('Operation failed');
})
).rejects.toThrow('Operation failed');
});
it('tracks consecutive failures', async () => {
const cb = new CircuitBreakerService('test', { consecutiveFailures: 3 });
// First two failures - circuit should stay closed
for (let i = 0; i < 2; i++) {
await expect(
cb.execute(async () => {
throw new Error('Failure');
})
).rejects.toThrow('Failure');
}
expect(cb.getState()).toBe('closed');
});
it('opens after consecutive failures threshold', async () => {
const cb = new CircuitBreakerService('test', { consecutiveFailures: 3 });
// Cause 3 consecutive failures to open the circuit
for (let i = 0; i < 3; i++) {
await expect(
cb.execute(async () => {
throw new Error('Failure');
})
).rejects.toThrow('Failure');
}
// Circuit should now be open
expect(cb.getState()).toBe('open');
expect(cb.isOpen()).toBe(true);
});
});
describe('state queries', () => {
it('getState() returns correct state', async () => {
const cb = new CircuitBreakerService('test', { consecutiveFailures: 2 });
expect(cb.getState()).toBe('closed');
// Open the circuit
for (let i = 0; i < 2; i++) {
try {
await cb.execute(async () => {
throw new Error('Fail');
});
} catch {
// Expected
}
}
expect(cb.getState()).toBe('open');
});
it('isOpen() returns correct boolean', async () => {
const cb = new CircuitBreakerService('test', { consecutiveFailures: 2 });
expect(cb.isOpen()).toBe(false);
// Open the circuit
for (let i = 0; i < 2; i++) {
try {
await cb.execute(async () => {
throw new Error('Fail');
});
} catch {
// Expected
}
}
expect(cb.isOpen()).toBe(true);
});
});
describe('configuration', () => {
it('accepts custom consecutiveFailures', async () => {
const cb = new CircuitBreakerService('test', { consecutiveFailures: 1 });
// Single failure should open the circuit
await expect(
cb.execute(async () => {
throw new Error('Fail');
})
).rejects.toThrow('Fail');
expect(cb.isOpen()).toBe(true);
});
it('accepts custom halfOpenAfter', () => {
// Just verify it accepts the config without error
const cb = new CircuitBreakerService('test', {
halfOpenAfter: 1000,
consecutiveFailures: 5,
});
expect(cb.getState()).toBe('closed');
});
});
describe('logging', () => {
it('logs state changes to stderr', async () => {
const cb = new CircuitBreakerService('test', { consecutiveFailures: 1 });
await expect(
cb.execute(async () => {
throw new Error('Fail');
})
).rejects.toThrow();
// Should have logged the state change
expect(stderrSpy).toHaveBeenCalled();
const calls = stderrSpy.mock.calls.map((c: unknown[]) => c[0] as string);
expect(calls.some((c) => c.includes('[CircuitBreaker:test]'))).toBe(true);
});
});
});
