telegram-ai-support/tests/utils/circuit-breaker.test.ts

import { describe, it, expect } from 'vitest';
import { CircuitBreaker, CircuitBreakerError, CircuitState } from '../../src/utils/circuit-breaker';

function sleep(ms: number): Promise<void> {
  return new Promise(resolve => setTimeout(resolve, ms));
}

describe('CircuitBreaker', () => {
  it('starts in CLOSED state', () => {
    const cb = new CircuitBreaker({ serviceName: 'test' });
    expect(cb.getState()).toBe(CircuitState.CLOSED);
  });

  it('passes through successful executions', async () => {
    const cb = new CircuitBreaker({ serviceName: 'test' });
    const result = await cb.execute(async () => 'ok');
    expect(result).toBe('ok');
    expect(cb.getState()).toBe(CircuitState.CLOSED);
  });

  it('opens after failure threshold is exceeded', async () => {
    const cb = new CircuitBreaker({
      serviceName: 'test',
      failureThreshold: 3,
      resetTimeoutMs: 100,
    });

    for (let i = 0; i < 3; i++) {
      await expect(cb.execute(async () => { throw new Error('fail'); })).rejects.toThrow('fail');
    }

    expect(cb.getState()).toBe(CircuitState.OPEN);
  });

  it('rejects requests while OPEN', async () => {
    const cb = new CircuitBreaker({
      serviceName: 'test',
      failureThreshold: 2,
      resetTimeoutMs: 5000,
    });

    // Trip the breaker
    for (let i = 0; i < 2; i++) {
      await expect(cb.execute(async () => { throw new Error('fail'); })).rejects.toThrow();
    }

    expect(cb.getState()).toBe(CircuitState.OPEN);

    // Should throw CircuitBreakerError
    await expect(cb.execute(async () => 'ok')).rejects.toThrow(CircuitBreakerError);
  });

  it('transitions to HALF_OPEN after reset timeout', async () => {
    const cb = new CircuitBreaker({
      serviceName: 'test',
      failureThreshold: 2,
      resetTimeoutMs: 100,
    });

    for (let i = 0; i < 2; i++) {
      await expect(cb.execute(async () => { throw new Error('fail'); })).rejects.toThrow();
    }
    expect(cb.getState()).toBe(CircuitState.OPEN);

    await sleep(150);

    // Next execute call checks the timeout and transitions to HALF_OPEN
    const result = await cb.execute(async () => 'recovered');
    expect(result).toBe('recovered');
    // Successful test in HALF_OPEN closes the circuit
    expect(cb.getState()).toBe(CircuitState.CLOSED);
  });

  it('closes after successful test in HALF_OPEN', async () => {
    const cb = new CircuitBreaker({
      serviceName: 'test',
      failureThreshold: 2,
      resetTimeoutMs: 100,
    });

    // Open the circuit
    for (let i = 0; i < 2; i++) {
      await expect(cb.execute(async () => { throw new Error('fail'); })).rejects.toThrow();
    }
    expect(cb.getState()).toBe(CircuitState.OPEN);

    // Wait for reset timeout
    await sleep(150);

    // Successful execution transitions HALF_OPEN -> CLOSED
    await cb.execute(async () => 'success');
    expect(cb.getState()).toBe(CircuitState.CLOSED);

    // Verify circuit is fully operational again
    const result = await cb.execute(async () => 'working');
    expect(result).toBe('working');
  });

  it('re-opens if HALF_OPEN test fails', async () => {
    const cb = new CircuitBreaker({
      serviceName: 'test',
      failureThreshold: 2,
      resetTimeoutMs: 100,
    });

    // Open the circuit
    for (let i = 0; i < 2; i++) {
      await expect(cb.execute(async () => { throw new Error('fail'); })).rejects.toThrow();
    }

    await sleep(150);

    // Fail during HALF_OPEN
    await expect(cb.execute(async () => { throw new Error('still broken'); })).rejects.toThrow();
    expect(cb.getState()).toBe(CircuitState.OPEN);
  });
});