/**
* Metrics Request Handler Tests (SMELL-001 God Object Refactor)
*
* TDD tests for MetricsRequestHandler extracted from MCPProxyServer.
* Tests written FIRST (RED phase), then implementation (GREEN phase).
*
* @see https://github.com/aberemia24/code-executor-MCP/issues/42
*/
import { describe, it, expect, beforeEach, vi } from 'vitest';
import { MetricsRequestHandler } from '../../src/handlers/metrics-request-handler.js';
import { MetricsExporter } from '../../src/metrics-exporter.js';
import type { IncomingMessage, ServerResponse } from 'http';
describe('MetricsRequestHandler', () => {
let handler: MetricsRequestHandler;
let metricsExporter: MetricsExporter;
let mockRequest: IncomingMessage;
let mockResponse: MockServerResponse;
beforeEach(() => {
metricsExporter = new MetricsExporter();
handler = new MetricsRequestHandler(metricsExporter);
// Mock request
mockRequest = {
method: 'GET',
url: '/metrics',
headers: {},
} as IncomingMessage;
// Mock response with captured output
mockResponse = createMockResponse();
});
describe('Happy Path', () => {
it('should_return200_when_metricsAvailable', async () => {
// Setup: Record some metrics
metricsExporter.recordCacheHit('schema');
metricsExporter.recordHttpRequest('GET', 200);
// Execute
await handler.handle(mockRequest, mockResponse, 'valid-token');
// Verify: 200 OK with Prometheus text format
expect(mockResponse.writeHead).toHaveBeenCalledWith(200, {
'Content-Type': 'text/plain; version=0.0.4',
});
expect(mockResponse.end).toHaveBeenCalled();
const body = getResponseBody(mockResponse);
expect(body).toContain('cache_hits_total');
expect(body).toContain('http_requests_total');
});
it('should_returnPrometheusFormat_when_successful', async () => {
await handler.handle(mockRequest, mockResponse, 'valid-token');
const body = getResponseBody(mockResponse);
// Prometheus format has HELP and TYPE comments
expect(body).toMatch(/# HELP/);
expect(body).toMatch(/# TYPE/);
});
it('should_includeAllMetrics_when_requested', async () => {
// Record various metrics
metricsExporter.recordCacheHit('schema');
metricsExporter.recordCacheMiss('schema');
metricsExporter.recordHttpRequest('GET', 200);
metricsExporter.recordHttpRequest('POST', 500);
await handler.handle(mockRequest, mockResponse, 'valid-token');
const body = getResponseBody(mockResponse);
// Verify all metric types present
expect(body).toContain('cache_hits_total');
expect(body).toContain('cache_misses_total');
expect(body).toContain('http_requests_total');
});
});
describe('Error Handling', () => {
it('should_return500_when_metricsExporterThrows', async () => {
// Setup: Mock metrics exporter failure
vi.spyOn(metricsExporter, 'getMetrics').mockRejectedValue(
new Error('Metrics export failed')
);
// Execute
await handler.handle(mockRequest, mockResponse, 'valid-token');
// Verify: 500 Internal Server Error with JSON error
expect(mockResponse.writeHead).toHaveBeenCalledWith(500, {
'Content-Type': 'application/json',
});
const body = JSON.parse(getResponseBody(mockResponse));
expect(body.error).toContain('Metrics request failed');
expect(body.error).toContain('Metrics export failed');
});
it('should_handleUnexpectedErrors_gracefully', async () => {
// Setup: Mock unexpected error type
vi.spyOn(metricsExporter, 'getMetrics').mockRejectedValue('string error');
// Execute
await handler.handle(mockRequest, mockResponse, 'valid-token');
// Verify: Still returns 500 with error message
expect(mockResponse.writeHead).toHaveBeenCalledWith(500, {
'Content-Type': 'application/json',
});
const body = JSON.parse(getResponseBody(mockResponse));
expect(body.error).toBeDefined();
});
});
describe('Integration with MetricsExporter', () => {
it('should_callGetMetrics_once', async () => {
const spy = vi.spyOn(metricsExporter, 'getMetrics');
await handler.handle(mockRequest, mockResponse, 'valid-token');
expect(spy).toHaveBeenCalledTimes(1);
});
it('should_returnEmptyMetrics_when_noMetricsRecorded', async () => {
// Fresh exporter with no metrics
const freshExporter = new MetricsExporter();
const freshHandler = new MetricsRequestHandler(freshExporter);
await freshHandler.handle(mockRequest, mockResponse, 'valid-token');
expect(mockResponse.writeHead).toHaveBeenCalledWith(200, {
'Content-Type': 'text/plain; version=0.0.4',
});
const body = getResponseBody(mockResponse);
// Should still have metric definitions, just zero values
expect(body).toBeTruthy();
});
});
describe('Authentication', () => {
it('should_receiveAuthToken_parameter', async () => {
// Handler receives pre-validated token from MCPProxyServer
// This test verifies the parameter is accepted
await handler.handle(mockRequest, mockResponse, 'test-auth-token');
// Verify handler executed successfully (auth already validated by proxy)
expect(mockResponse.writeHead).toHaveBeenCalled();
});
});
});
// ============================================================================
// Test Helpers
// ============================================================================
/**
* Mock ServerResponse that captures output
*/
interface MockServerResponse extends ServerResponse {
_chunks: string[];
}
function createMockResponse(): MockServerResponse {
const chunks: string[] = [];
const mock = {
writeHead: vi.fn(),
end: vi.fn((data?: string) => {
if (data) chunks.push(data);
}),
_chunks: chunks,
} as unknown as MockServerResponse;
return mock;
}
function getResponseBody(res: MockServerResponse): string {
return res._chunks.join('');
}
