Skip TracingChannel tests on Node < 19.9

Node 18 backported TracingChannel but with a buggy implementation —
unsubscribing and resubscribing to the same channel crashes internally
(`_subscribers` becomes undefined). Node 16 has no TracingChannel at all.

Gate tests on `hasStableTracingChannel` which checks both that
`dc.tracingChannel` exists AND that the aggregated `hasSubscribers`
getter returns a boolean (only true on Node 19.9+/20.5+).

TracingChannel tests: skipped on Node 16/18, run on Node 20+
Plain channel tests (release/remove): run on all versions

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

Author: logaretm

packages/pg-pool/test/diagnostics.js

@@ -7,6 +7,12 @@ const it = require('mocha').it
 const dc = require('diagnostics_channel')
 const Pool = require('../')
 
+// TracingChannel exists on Node 18+ but the aggregated hasSubscribers getter
+// and stable unsubscribe behavior require Node 19.9+/20.5+. Skip tracing
+// tests on older versions where TracingChannel is missing or has internal bugs.
+const hasStableTracingChannel =
+  typeof dc.tracingChannel === 'function' && typeof dc.tracingChannel('pg:pool:test:probe').hasSubscribers === 'boolean'
+
 function mockClient(methods) {
   return function () {
     const client = new EventEmitter()
@@ -23,7 +29,7 @@ function mockClient(methods) {
 
 describe('diagnostics channels', function () {
   describe('pg:pool:connect', function () {
-    it('publishes start event when connect is called', function (done) {
+    ;(hasStableTracingChannel ? it : it.skip)('publishes start event when connect is called', function (done) {
       const pool = new Pool({
         Client: mockClient({
           connect: function (cb) {
@@ -60,7 +66,7 @@ describe('diagnostics channels', function () {
         })
       })
     })
-    it('enriches context with client info on asyncEnd', function (done) {
+    ;(hasStableTracingChannel ? it : it.skip)('enriches context with client info on asyncEnd', function (done) {
       const pool = new Pool({
         Client: mockClient({
           connect: function (cb) {

packages/pg/test/unit/client/diagnostics-tests.js

@@ -3,11 +3,19 @@ const helper = require('./test-helper')
 const assert = require('assert')
 const dc = require('diagnostics_channel')
 
+// TracingChannel exists on Node 18+ but the aggregated hasSubscribers getter
+// and stable unsubscribe behavior require Node 19.9+/20.5+. Skip tests on
+// older versions where TracingChannel is missing or has internal bugs.
+const hasStableTracingChannel =
+  typeof dc.tracingChannel === 'function' && typeof dc.tracingChannel('pg:test:probe').hasSubscribers === 'boolean'
+
 const suite = new helper.Suite()
 const test = suite.test.bind(suite)
+// pass undefined as callback to skip when TracingChannel is unavailable/unstable
+const testTracing = (name, cb) => test(name, hasStableTracingChannel ? cb : undefined)
 
-test('query diagnostics channel', function () {
-  test('publishes start and asyncEnd on successful query', function (done) {
+testTracing('query diagnostics channel', function () {
+  testTracing('publishes start and asyncEnd on successful query', function (done) {
     const client = helper.client()
     client.connection.emit('readyForQuery')
 
@@ -50,7 +58,7 @@ test('query diagnostics channel', function () {
     client.connection.emit('readyForQuery')
   })
 
-  test('publishes error on failed query', function (done) {
+  testTracing('publishes error on failed query', function (done) {
     const client = helper.client()
     client.connection.emit('readyForQuery')
 
@@ -87,7 +95,7 @@ test('query diagnostics channel', function () {
     })
   })
 
-  test('query context includes client info', function (done) {
+  testTracing('query context includes client info', function (done) {
     const client = helper.client({ database: 'testdb', host: 'localhost', port: 5432, user: 'testuser' })
     client.connection.emit('readyForQuery')
 
@@ -120,7 +128,7 @@ test('query diagnostics channel', function () {
     client.connection.emit('readyForQuery')
   })
 
-  test('promise query publishes diagnostics', function (done) {
+  testTracing('promise query publishes diagnostics', function (done) {
     const client = helper.client()
     client.connection.emit('readyForQuery')
 
@@ -154,8 +162,8 @@ test('query diagnostics channel', function () {
   })
 })
 
-test('connection diagnostics channel', function () {
-  test('publishes start on connect with callback', function (done) {
+testTracing('connection diagnostics channel', function () {
+  testTracing('publishes start on connect with callback', function (done) {
     const Connection = require('../../../lib/connection')
     const { Client } = helper