address reviewer feedback: use skip() instead of exit, export dc for testability

- Replace process.exit(0) with poku's skip() for better test reporting
- Export dc and hasTracingChannel from tracing.js for testing
- Add unit test for tracing module (dc availability, channel setup, getServerContext)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: logaretm

lib/tracing.d.ts

@@ -29,6 +29,9 @@ export interface PoolConnectTraceContext {
   serverPort: number | undefined;
 }
 
+export declare const dc: typeof import('node:diagnostics_channel') | undefined;
+export declare const hasTracingChannel: boolean;
+
 export declare const queryChannel:
   | TracingChannel<QueryTraceContext>
   | undefined;

lib/tracing.js

@@ -70,6 +70,8 @@ function tracePoolConnect(fn, contextFactory) {
 }
 
 module.exports = {
+  dc,
+  hasTracingChannel,
   queryChannel,
   executeChannel,
   connectChannel,

test/integration/tracing-channel.test.mts

@@ -6,15 +6,14 @@ import type {
 } from '../../lib/tracing.js';
 import type { RowDataPacket } from '../../promise.js';
 import diagnostics_channel from 'node:diagnostics_channel';
-import { assert, describe, it } from 'poku';
+import { assert, describe, it, skip } from 'poku';
 import { config, createConnection, createPool } from '../common.test.mjs';
 
 const hasTracingChannel =
   typeof diagnostics_channel.tracingChannel === 'function';
 
 if (!hasTracingChannel) {
-  // TracingChannel requires Node 19.9+ / 20+
-  process.exit(0);
+  skip('TracingChannel requires Node 19.9+ / 20+');
 }
 
 interface TraceEvent<T> {

test/unit/test-tracing.test.mts

@@ -0,0 +1,48 @@
+import { describe, it, strict } from 'poku';
+import tracing from '../../lib/tracing.js';
+
+const { dc, hasTracingChannel } = tracing;
+
+await describe('Tracing module', async () => {
+  await it('should load diagnostics_channel', () => {
+    // dc should be defined on Node.js versions that support diagnostics_channel
+    strict.ok(
+      dc !== undefined,
+      'diagnostics_channel should be available'
+    );
+  });
+
+  await it('should detect TracingChannel support', () => {
+    if (typeof dc?.tracingChannel === 'function') {
+      strict.ok(hasTracingChannel, 'hasTracingChannel should be true when tracingChannel exists');
+      strict.ok(tracing.queryChannel !== undefined, 'queryChannel should be defined');
+      strict.ok(tracing.executeChannel !== undefined, 'executeChannel should be defined');
+      strict.ok(tracing.connectChannel !== undefined, 'connectChannel should be defined');
+      strict.ok(tracing.poolConnectChannel !== undefined, 'poolConnectChannel should be defined');
+    } else {
+      strict.ok(!hasTracingChannel, 'hasTracingChannel should be false when tracingChannel is unavailable');
+      strict.strictEqual(tracing.queryChannel, undefined, 'queryChannel should be undefined');
+      strict.strictEqual(tracing.executeChannel, undefined, 'executeChannel should be undefined');
+      strict.strictEqual(tracing.connectChannel, undefined, 'connectChannel should be undefined');
+      strict.strictEqual(tracing.poolConnectChannel, undefined, 'poolConnectChannel should be undefined');
+    }
+  });
+
+  await it('should return server context for host/port', () => {
+    const ctx = tracing.getServerContext({ host: '127.0.0.1', port: 3307 });
+    strict.strictEqual(ctx.serverAddress, '127.0.0.1');
+    strict.strictEqual(ctx.serverPort, 3307);
+  });
+
+  await it('should return server context for socketPath', () => {
+    const ctx = tracing.getServerContext({ socketPath: '/tmp/mysql.sock' });
+    strict.strictEqual(ctx.serverAddress, '/tmp/mysql.sock');
+    strict.strictEqual(ctx.serverPort, undefined);
+  });
+
+  await it('should default to localhost:3306', () => {
+    const ctx = tracing.getServerContext({});
+    strict.strictEqual(ctx.serverAddress, 'localhost');
+    strict.strictEqual(ctx.serverPort, 3306);
+  });
+});