diff --git a/test/node-test/diagnostics-channel/connect-error.js b/test/node-test/diagnostics-channel/connect-error.js
new file mode 100644
index 00000000000..35559fab86a
--- /dev/null
+++ b/test/node-test/diagnostics-channel/connect-error.js
@@ -0,0 +1,65 @@
+'use strict'
+
+const { test, skip } = require('node:test')
+const { tspl } = require('@matteo.collina/tspl')
+
+let diagnosticsChannel
+
+try {
+  diagnosticsChannel = require('diagnostics_channel')
+} catch {
+  skip('missing diagnostics_channel')
+  process.exit(0)
+}
+
+const { Client } = require('../../..')
+
+test('Diagnostics channel - connect error', (t) => {
+  const connectError = new Error('custom error')
+  const assert = tspl(t, { plan: 16 })
+
+  let _connector
+  diagnosticsChannel.channel('undici:client:beforeConnect').subscribe(({ connectParams, connector }) => {
+    _connector = connector
+
+    assert.equal(typeof _connector, 'function')
+    assert.equal(Object.keys(connectParams).length, 6)
+
+    const { host, hostname, protocol, port, servername } = connectParams
+
+    assert.equal(host, 'localhost:1234')
+    assert.equal(hostname, 'localhost')
+    assert.equal(port, '1234')
+    assert.equal(protocol, 'http:')
+    assert.equal(servername, null)
+  })
+
+  diagnosticsChannel.channel('undici:client:connectError').subscribe(({ error, connectParams, connector }) => {
+    assert.equal(Object.keys(connectParams).length, 6)
+    assert.equal(_connector, connector)
+
+    const { host, hostname, protocol, port, servername } = connectParams
+
+    assert.equal(error, connectError)
+    assert.equal(host, 'localhost:1234')
+    assert.equal(hostname, 'localhost')
+    assert.equal(port, '1234')
+    assert.equal(protocol, 'http:')
+    assert.equal(servername, null)
+  })
+
+  const client = new Client('http://localhost:1234', {
+    connect: (_, cb) => { cb(connectError, null) }
+  })
+
+  return new Promise((resolve) => {
+    client.request({
+      path: '/',
+      method: 'GET'
+    }, (err, data) => {
+      assert.equal(err, connectError)
+      client.close()
+      resolve()
+    })
+  })
+})
diff --git a/test/node-test/diagnostics-channel/error.js b/test/node-test/diagnostics-channel/error.js
new file mode 100644
index 00000000000..2a737d70b33
--- /dev/null
+++ b/test/node-test/diagnostics-channel/error.js
@@ -0,0 +1,57 @@
+'use strict'
+
+const { test, skip, after } = require('node:test')
+const { tspl } = require('@matteo.collina/tspl')
+
+let diagnosticsChannel
+
+try {
+  diagnosticsChannel = require('diagnostics_channel')
+} catch {
+  skip('missing diagnostics_channel')
+  process.exit(0)
+}
+
+const { Client } = require('../..')
+const { createServer } = require('http')
+
+test('Diagnostics channel - error', (t) => {
+  const assert = tspl(t, { plan: 3 })
+  const server = createServer((req, res) => {
+    res.destroy()
+  })
+  after(server.close.bind(server))
+
+  const reqHeaders = {
+    foo: undefined,
+    bar: 'bar'
+  }
+
+  let _req
+  diagnosticsChannel.channel('undici:request:create').subscribe(({ request }) => {
+    _req = request
+  })
+
+  diagnosticsChannel.channel('undici:request:error').subscribe(({ request, error }) => {
+    assert.equal(_req, request)
+    assert.equal(error.code, 'UND_ERR_SOCKET')
+  })
+
+  return new Promise((resolve) => {
+    server.listen(0, () => {
+      const client = new Client(`http://localhost:${server.address().port}`, {
+        keepAliveTimeout: 300e3
+      })
+
+      client.request({
+        path: '/',
+        method: 'GET',
+        headers: reqHeaders
+      }, (err, data) => {
+        assert.equal(err.code, 'UND_ERR_SOCKET')
+        client.close()
+        resolve()
+      })
+    })
+  })
+})
diff --git a/test/node-test/diagnostics-channel/get.js b/test/node-test/diagnostics-channel/get.js
new file mode 100644
index 00000000000..e0feeb2fe56
--- /dev/null
+++ b/test/node-test/diagnostics-channel/get.js
@@ -0,0 +1,149 @@
+'use strict'
+
+const { test, skip, after } = require('node:test')
+const { tspl } = require('@matteo.collina/tspl')
+
+let diagnosticsChannel
+
+try {
+  diagnosticsChannel = require('diagnostics_channel')
+} catch {
+  skip('missing diagnostics_channel')
+  process.exit(0)
+}
+
+const { Client } = require('../..')
+const { createServer } = require('http')
+
+test('Diagnostics channel - get', (t) => {
+  const assert = tspl(t, { plan: 32 })
+  const server = createServer((req, res) => {
+    res.setHeader('Content-Type', 'text/plain')
+    res.setHeader('trailer', 'foo')
+    res.write('hello')
+    res.addTrailers({
+      foo: 'oof'
+    })
+    res.end()
+  })
+
+  after(server.close.bind(server))
+
+  const reqHeaders = {
+    foo: undefined,
+    bar: 'bar'
+  }
+
+  let _req
+  diagnosticsChannel.channel('undici:request:create').subscribe(({ request }) => {
+    _req = request
+    assert.equal(request.origin, `http://localhost:${server.address().port}`)
+    assert.equal(request.completed, false)
+    assert.equal(request.method, 'GET')
+    assert.equal(request.path, '/')
+    assert.equal(request.headers, 'bar: bar\r\n')
+    request.addHeader('hello', 'world')
+    assert.equal(request.headers, 'bar: bar\r\nhello: world\r\n')
+  })
+
+  let _connector
+  diagnosticsChannel.channel('undici:client:beforeConnect').subscribe(({ connectParams, connector }) => {
+    _connector = connector
+
+    assert.equal(typeof _connector, 'function')
+    assert.equal(Object.keys(connectParams).length, 6)
+
+    const { host, hostname, protocol, port, servername } = connectParams
+
+    assert.equal(host, `localhost:${server.address().port}`)
+    assert.equal(hostname, 'localhost')
+    assert.equal(port, String(server.address().port))
+    assert.equal(protocol, 'http:')
+    assert.equal(servername, null)
+  })
+
+  let _socket
+  diagnosticsChannel.channel('undici:client:connected').subscribe(({ connectParams, socket, connector }) => {
+    _socket = socket
+
+    assert.equal(_connector, connector)
+    assert.equal(Object.keys(connectParams).length, 6)
+
+    const { host, hostname, protocol, port, servername } = connectParams
+
+    assert.equal(host, `localhost:${server.address().port}`)
+    assert.equal(hostname, 'localhost')
+    assert.equal(port, String(server.address().port))
+    assert.equal(protocol, 'http:')
+    assert.equal(servername, null)
+  })
+
+  diagnosticsChannel.channel('undici:client:sendHeaders').subscribe(({ request, headers, socket }) => {
+    assert.equal(_req, request)
+    assert.equal(_socket, socket)
+
+    const expectedHeaders = [
+      'GET / HTTP/1.1',
+      `host: localhost:${server.address().port}`,
+      'connection: keep-alive',
+      'bar: bar',
+      'hello: world'
+    ]
+
+    assert.equal(headers, expectedHeaders.join('\r\n') + '\r\n')
+  })
+
+  diagnosticsChannel.channel('undici:request:headers').subscribe(({ request, response }) => {
+    assert.equal(_req, request)
+    assert.equal(response.statusCode, 200)
+    const expectedHeaders = [
+      Buffer.from('Content-Type'),
+      Buffer.from('text/plain'),
+      Buffer.from('trailer'),
+      Buffer.from('foo'),
+      Buffer.from('Date'),
+      response.headers[5], // This is a date
+      Buffer.from('Connection'),
+      Buffer.from('keep-alive'),
+      Buffer.from('Keep-Alive'),
+      Buffer.from('timeout=5'),
+      Buffer.from('Transfer-Encoding'),
+      Buffer.from('chunked')
+    ]
+    assert.deepStrictEqual(response.headers, expectedHeaders)
+    assert.equal(response.statusText, 'OK')
+  })
+
+  let endEmitted = false
+
+  return new Promise((resolve) => {
+    diagnosticsChannel.channel('undici:request:trailers').subscribe(({ request, trailers }) => {
+      assert.equal(request.completed, true)
+      assert.equal(_req, request)
+      // This event is emitted after the last chunk has been added to the body stream,
+      // not when it was consumed by the application
+      assert.equal(endEmitted, false)
+      assert.deepStrictEqual(trailers, [Buffer.from('foo'), Buffer.from('oof')])
+      resolve()
+    })
+
+    server.listen(0, () => {
+      const client = new Client(`http://localhost:${server.address().port}`, {
+        keepAliveTimeout: 300e3
+      })
+
+      client.request({
+        path: '/',
+        method: 'GET',
+        headers: reqHeaders
+      }, (err, data) => {
+        assert.ok(!err)
+        client.close()
+
+        data.body.on('end', function () {
+          endEmitted = true
+        })
+      })
+    })
+  })
+})
diff --git a/test/node-test/diagnostics-channel/post-stream.js b/test/node-test/diagnostics-channel/post-stream.js
new file mode 100644
index 00000000000..3510e74993b
--- /dev/null
+++ b/test/node-test/diagnostics-channel/post-stream.js
@@ -0,0 +1,155 @@
+'use strict'
+
+const { test, skip, after } = require('node:test')
+const { tspl } = require('@matteo.collina/tspl')
+const { Readable } = require('stream')
+
+let diagnosticsChannel
+
+try {
+  diagnosticsChannel = require('diagnostics_channel')
+} catch {
+  skip('missing diagnostics_channel')
+  process.exit(0)
+}
+
+const { Client } = require('../..')
+const { createServer } = require('http')
+
+test('Diagnostics channel - post stream', (t) => {
+  const assert = tspl(t, { plan: 33 })
+  const server = createServer((req, res) => {
+    req.resume()
+    res.setHeader('Content-Type', 'text/plain')
+    res.setHeader('trailer', 'foo')
+    res.write('hello')
+    res.addTrailers({
+      foo: 'oof'
+    })
+    res.end()
+  })
+  after(server.close.bind(server))
+
+  const reqHeaders = {
+    foo: undefined,
+    bar: 'bar'
+  }
+  const body = Readable.from(['hello', ' ', 'world'])
+
+  let _req
+  diagnosticsChannel.channel('undici:request:create').subscribe(({ request }) => {
+    _req = request
+    assert.equal(request.completed, false)
+    assert.equal(request.method, 'POST')
+    assert.equal(request.path, '/')
+    assert.equal(request.headers, 'bar: bar\r\n')
+    request.addHeader('hello', 'world')
+    assert.equal(request.headers, 'bar: bar\r\nhello: world\r\n')
+    assert.deepStrictEqual(request.body, body)
+  })
+
+  let _connector
+  diagnosticsChannel.channel('undici:client:beforeConnect').subscribe(({ connectParams, connector }) => {
+    _connector = connector
+
+    assert.equal(typeof _connector, 'function')
+    assert.equal(Object.keys(connectParams).length, 6)
+
+    const { host, hostname, protocol, port, servername } = connectParams
+
+    assert.equal(host, `localhost:${server.address().port}`)
+    assert.equal(hostname, 'localhost')
+    assert.equal(port, String(server.address().port))
+    assert.equal(protocol, 'http:')
+    assert.equal(servername, null)
+  })
+
+  let _socket
+  diagnosticsChannel.channel('undici:client:connected').subscribe(({ connectParams, socket, connector }) => {
+    _socket = socket
+
+    assert.equal(Object.keys(connectParams).length, 6)
+    assert.equal(_connector, connector)
+
+    const { host, hostname, protocol, port, servername } = connectParams
+
+    assert.equal(host, `localhost:${server.address().port}`)
+    assert.equal(hostname, 'localhost')
+    assert.equal(port, String(server.address().port))
+    assert.equal(protocol, 'http:')
+    assert.equal(servername, null)
+  })
+
+  diagnosticsChannel.channel('undici:client:sendHeaders').subscribe(({ request, headers, socket }) => {
+    assert.equal(_req, request)
+    assert.equal(_socket, socket)
+
+    const expectedHeaders = [
+      'POST / HTTP/1.1',
+      `host: localhost:${server.address().port}`,
+      'connection: keep-alive',
+      'bar: bar',
+      'hello: world'
+    ]
+
+    assert.equal(headers, expectedHeaders.join('\r\n') + '\r\n')
+  })
+
+  diagnosticsChannel.channel('undici:request:headers').subscribe(({ request, response }) => {
+    assert.equal(_req, request)
+    assert.equal(response.statusCode, 200)
+    const expectedHeaders = [
+      Buffer.from('Content-Type'),
+      Buffer.from('text/plain'),
+      Buffer.from('trailer'),
+      Buffer.from('foo'),
+      Buffer.from('Date'),
+      response.headers[5], // This is a date
+      Buffer.from('Connection'),
+      Buffer.from('keep-alive'),
+      Buffer.from('Keep-Alive'),
+      Buffer.from('timeout=5'),
+      Buffer.from('Transfer-Encoding'),
+      Buffer.from('chunked')
+    ]
+    assert.deepStrictEqual(response.headers, expectedHeaders)
+    assert.equal(response.statusText, 'OK')
+  })
+
+  diagnosticsChannel.channel('undici:request:bodySent').subscribe(({ request }) => {
+    assert.equal(_req, request)
+  })
+
+  let endEmitted = false
+
+  return new Promise((resolve) => {
+    diagnosticsChannel.channel('undici:request:trailers').subscribe(({ request, trailers }) => {
+      assert.equal(request.completed, true)
+      assert.equal(_req, request)
+      // This event is emitted after the last chunk has been added to the body stream,
+      // not when it was consumed by the application
+      assert.equal(endEmitted, false)
+      assert.deepStrictEqual(trailers, [Buffer.from('foo'), Buffer.from('oof')])
+      resolve()
+    })
+
+    server.listen(0, () => {
+      const client = new Client(`http://localhost:${server.address().port}`, {
+        keepAliveTimeout: 300e3
+      })
+
+      client.request({
+        path: '/',
+        method: 'POST',
+        headers: reqHeaders,
+        body
+      }, (err, data) => {
+        assert.ok(!err)
+        client.close()
+        data.body.on('end', function () {
+          endEmitted = true
+        })
+      })
+    })
+  })
+})
diff --git a/test/node-test/diagnostics-channel/post.js b/test/node-test/diagnostics-channel/post.js
new file mode 100644
index 00000000000..1f0475bd556
--- /dev/null
+++ b/test/node-test/diagnostics-channel/post.js
@@ -0,0 +1,154 @@
+'use strict'
+
+const { test, skip, after } = require('node:test')
+const { tspl } = require('@matteo.collina/tspl')
+
+let diagnosticsChannel
+
+try {
+  diagnosticsChannel = require('diagnostics_channel')
+} catch {
+  skip('missing diagnostics_channel')
+  process.exit(0)
+}
+
+const { Client } = require('../../..')
+const { createServer } = require('http')
+
+test('Diagnostics channel - post', (t) => {
+  const assert = tspl(t, { plan: 33 })
+  const server = createServer((req, res) => {
+    req.resume()
+    res.setHeader('Content-Type', 'text/plain')
+    res.setHeader('trailer', 'foo')
+    res.write('hello')
+    res.addTrailers({
+      foo: 'oof'
+    })
+    res.end()
+  })
+  after(server.close.bind(server))
+
+  const reqHeaders = {
+    foo: undefined,
+    bar: 'bar'
+  }
+
+  let _req
+  diagnosticsChannel.channel('undici:request:create').subscribe(({ request }) => {
+    _req = request
+    assert.equal(request.completed, false)
+    assert.equal(request.method, 'POST')
+    assert.equal(request.path, '/')
+    assert.equal(request.headers, 'bar: bar\r\n')
+    request.addHeader('hello', 'world')
+    assert.equal(request.headers, 'bar: bar\r\nhello: world\r\n')
+    assert.deepStrictEqual(request.body, Buffer.from('hello world'))
+  })
+
+  let _connector
+  diagnosticsChannel.channel('undici:client:beforeConnect').subscribe(({ connectParams, connector }) => {
+    _connector = connector
+
+    assert.equal(typeof _connector, 'function')
+    assert.equal(Object.keys(connectParams).length, 6)
+
+    const { host, hostname, protocol, port, servername } = connectParams
+
+    assert.equal(host, `localhost:${server.address().port}`)
+    assert.equal(hostname, 'localhost')
+    assert.equal(port, String(server.address().port))
+    assert.equal(protocol, 'http:')
+    assert.equal(servername, null)
+  })
+
+  let _socket
+  diagnosticsChannel.channel('undici:client:connected').subscribe(({ connectParams, socket, connector }) => {
+    _socket = socket
+
+    assert.equal(Object.keys(connectParams).length, 6)
+    assert.equal(_connector, connector)
+
+    const { host, hostname, protocol, port, servername } = connectParams
+
+    assert.equal(host, `localhost:${server.address().port}`)
+    assert.equal(hostname, 'localhost')
+    assert.equal(port, String(server.address().port))
+    assert.equal(protocol, 'http:')
+    assert.equal(servername, null)
+  })
+
+  diagnosticsChannel.channel('undici:client:sendHeaders').subscribe(({ request, headers, socket }) => {
+    assert.equal(_req, request)
+    assert.equal(_socket, socket)
+
+    const expectedHeaders = [
+      'POST / HTTP/1.1',
+      `host: localhost:${server.address().port}`,
+      'connection: keep-alive',
+      'bar: bar',
+      'hello: world'
+    ]
+
+    assert.equal(headers, expectedHeaders.join('\r\n') + '\r\n')
+  })
+
+  diagnosticsChannel.channel('undici:request:headers').subscribe(({ request, response }) => {
+    assert.equal(_req, request)
+    assert.equal(response.statusCode, 200)
+    const expectedHeaders = [
+      Buffer.from('Content-Type'),
+      Buffer.from('text/plain'),
+      Buffer.from('trailer'),
+      Buffer.from('foo'),
+      Buffer.from('Date'),
+      response.headers[5], // This is a date
+      Buffer.from('Connection'),
+      Buffer.from('keep-alive'),
+      Buffer.from('Keep-Alive'),
+      Buffer.from('timeout=5'),
+      Buffer.from('Transfer-Encoding'),
+      Buffer.from('chunked')
+    ]
+    assert.deepStrictEqual(response.headers, expectedHeaders)
+    assert.equal(response.statusText, 'OK')
+  })
+
+  diagnosticsChannel.channel('undici:request:bodySent').subscribe(({ request }) => {
+    assert.equal(_req, request)
+  })
+
+  let endEmitted = false
+
+  return new Promise((resolve) => {
+    diagnosticsChannel.channel('undici:request:trailers').subscribe(({ request, trailers }) => {
+      assert.equal(request.completed, true)
+      assert.equal(_req, request)
+      // This event is emitted after the last chunk has been added to the body stream,
+      // not when it was consumed by the application
+      assert.equal(endEmitted, false)
+      assert.deepStrictEqual(trailers, [Buffer.from('foo'), Buffer.from('oof')])
+      resolve()
+    })
+
+    server.listen(0, () => {
+      const client = new Client(`http://localhost:${server.address().port}`, {
+        keepAliveTimeout: 300e3
+      })
+
+      client.request({
+        path: '/',
+        method: 'POST',
+        headers: reqHeaders,
+        body: 'hello world'
+      }, (err, data) => {
+        assert.ok(!err)
+        client.close()
+
+        data.body.on('end', function () {
+          endEmitted = true
+        })
+      })
+    })
+  })
+})