Merge branch 'main' into change-module-path-to-sneak-berlin

internal/ircserver/integration_test.go

@@ -0,0 +1,913 @@
+package ircserver_test
+
+import (
+	"strings"
+	"testing"
+	"time"
+)
+
+// TestIntegrationTwoClients is a comprehensive integration
+// test that spawns the IRC server programmatically, connects
+// two real TCP clients, and verifies all major IRC features
+// including cross-client message delivery.
+//
+// The test runs sequentially through IRC features because
+// both clients share the same channel state.  Each section
+// builds on the previous one (e.g. alice and bob must be
+// JOINed before PRIVMSG can be tested).
+//
+//nolint:cyclop,funlen,maintidx // integration test
+func TestIntegrationTwoClients(t *testing.T) {
+	t.Parallel()
+
+	env := newTestEnv(t)
+
+	alice := env.dial(t)
+	bob := env.dial(t)
+
+	// ── Registration ──────────────────────────────────
+
+	aliceWelcome := alice.register("alice")
+	assertContains(
+		t, aliceWelcome, " 001 ", "RPL_WELCOME alice",
+	)
+	assertContains(
+		t, aliceWelcome, " 002 ", "RPL_YOURHOST alice",
+	)
+	assertContains(
+		t, aliceWelcome, " 003 ", "RPL_CREATED alice",
+	)
+	assertContains(
+		t, aliceWelcome, " 004 ", "RPL_MYINFO alice",
+	)
+	assertContains(
+		t, aliceWelcome, "alice",
+		"nick in welcome burst",
+	)
+
+	bobWelcome := bob.register("bob")
+	assertContains(
+		t, bobWelcome, " 001 ", "RPL_WELCOME bob",
+	)
+	assertContains(
+		t, bobWelcome, "bob",
+		"nick in welcome burst",
+	)
+
+	// ── JOIN and cross-client visibility ──────────────
+
+	alice.send("JOIN #integration")
+	aliceJoinLines := alice.readUntil(func(l string) bool {
+		return strings.Contains(l, " 366 ")
+	})
+	assertContains(
+		t, aliceJoinLines, "JOIN",
+		"alice receives JOIN echo",
+	)
+	assertContains(
+		t, aliceJoinLines, " 366 ",
+		"RPL_ENDOFNAMES for alice",
+	)
+
+	bob.send("JOIN #integration")
+	bobJoinLines := bob.readUntil(func(l string) bool {
+		return strings.Contains(l, " 366 ")
+	})
+	assertContains(
+		t, bobJoinLines, "JOIN",
+		"bob receives JOIN echo",
+	)
+
+	// Alice should see bob's JOIN via relay.
+	aliceSeesBob := alice.readUntil(func(l string) bool {
+		return strings.Contains(l, "JOIN") &&
+			strings.Contains(l, "bob")
+	})
+	assertContains(
+		t, aliceSeesBob, "bob",
+		"alice sees bob's JOIN",
+	)
+
+	// ── PRIVMSG (channel) — alice to bob ──────────────
+
+	alice.send("PRIVMSG #integration :hello from alice")
+
+	bobGetsMsg := bob.readUntil(func(l string) bool {
+		return strings.Contains(l, "hello from alice")
+	})
+	assertContains(
+		t, bobGetsMsg, "hello from alice",
+		"bob receives alice's channel message",
+	)
+
+	// ── PRIVMSG (channel) — bob to alice ──────────────
+
+	bob.send("PRIVMSG #integration :hello from bob")
+
+	aliceGetsMsg := alice.readUntil(func(l string) bool {
+		return strings.Contains(l, "hello from bob")
+	})
+	assertContains(
+		t, aliceGetsMsg, "hello from bob",
+		"alice receives bob's channel message",
+	)
+
+	// ── PRIVMSG (DM) — alice to bob ──────────────────
+
+	alice.send("PRIVMSG bob :secret message")
+
+	bobDM := bob.readUntil(func(l string) bool {
+		return strings.Contains(l, "secret message")
+	})
+	assertContains(
+		t, bobDM, "secret message",
+		"bob receives alice's DM",
+	)
+	assertContains(
+		t, bobDM, "alice",
+		"DM from field is alice",
+	)
+
+	// ── PRIVMSG (DM) — bob to alice ──────────────────
+
+	bob.send("PRIVMSG alice :reply to you")
+
+	aliceDM := alice.readUntil(func(l string) bool {
+		return strings.Contains(l, "reply to you")
+	})
+	assertContains(
+		t, aliceDM, "reply to you",
+		"alice receives bob's DM",
+	)
+
+	// ── NOTICE (channel) ──────────────────────────────
+
+	alice.send("NOTICE #integration :notice msg")
+
+	bobNotice := bob.readUntil(func(l string) bool {
+		return strings.Contains(l, "notice msg")
+	})
+	assertContains(
+		t, bobNotice, "NOTICE",
+		"bob receives NOTICE command",
+	)
+	assertContains(
+		t, bobNotice, "notice msg",
+		"bob receives NOTICE text",
+	)
+
+	// ── NOTICE (DM) ──────────────────────────────────
+
+	bob.send("NOTICE alice :dm notice")
+
+	aliceNotice := alice.readUntil(func(l string) bool {
+		return strings.Contains(l, "dm notice")
+	})
+	assertContains(
+		t, aliceNotice, "dm notice",
+		"alice receives DM NOTICE",
+	)
+
+	// ── TOPIC ─────────────────────────────────────────
+	// alice is the channel creator so she is +o.
+
+	alice.send("TOPIC #integration :Integration Test Topic")
+
+	aliceTopic := alice.readUntil(func(l string) bool {
+		return strings.Contains(
+			l, "Integration Test Topic",
+		)
+	})
+	assertContains(
+		t, aliceTopic, "Integration Test Topic",
+		"alice sees TOPIC echo",
+	)
+
+	bobTopic := bob.readUntil(func(l string) bool {
+		return strings.Contains(
+			l, "Integration Test Topic",
+		)
+	})
+	assertContains(
+		t, bobTopic, "Integration Test Topic",
+		"bob receives TOPIC change",
+	)
+
+	// ── MODE (query) ──────────────────────────────────
+
+	alice.send("MODE #integration")
+
+	aliceMode := alice.readUntil(func(l string) bool {
+		return strings.Contains(l, " 324 ")
+	})
+	assertContains(
+		t, aliceMode, " 324 ",
+		"RPL_CHANNELMODEIS",
+	)
+
+	// ── MODE (+m moderated, then -m) ──────────────────
+
+	alice.send("MODE #integration +m")
+
+	aliceModeM := alice.readUntil(func(l string) bool {
+		return strings.Contains(l, "MODE") &&
+			strings.Contains(l, "+m")
+	})
+	assertContains(
+		t, aliceModeM, "+m",
+		"alice sees MODE +m echo",
+	)
+
+	bobModeM := bob.readUntil(func(l string) bool {
+		return strings.Contains(l, "+m")
+	})
+	assertContains(
+		t, bobModeM, "+m",
+		"bob sees MODE +m relay",
+	)
+
+	// Revert moderated mode.
+	alice.send("MODE #integration -m")
+	alice.readUntil(func(l string) bool {
+		return strings.Contains(l, "-m")
+	})
+	bob.readUntil(func(l string) bool {
+		return strings.Contains(l, "-m")
+	})
+
+	// ── MODE (+v voice, then -v) ──────────────────────
+
+	alice.send("MODE #integration +v bob")
+
+	aliceVoice := alice.readUntil(func(l string) bool {
+		return strings.Contains(l, "+v")
+	})
+	assertContains(
+		t, aliceVoice, "+v",
+		"alice sees +v echo",
+	)
+
+	bobVoice := bob.readUntil(func(l string) bool {
+		return strings.Contains(l, "+v")
+	})
+	assertContains(
+		t, bobVoice, "+v",
+		"bob receives +v relay",
+	)
+
+	// Remove voice.
+	alice.send("MODE #integration -v bob")
+	alice.readUntil(func(l string) bool {
+		return strings.Contains(l, "-v")
+	})
+	bob.readUntil(func(l string) bool {
+		return strings.Contains(l, "-v")
+	})
+
+	// ── NAMES ─────────────────────────────────────────
+
+	alice.send("NAMES #integration")
+
+	aliceNames := alice.readUntil(func(l string) bool {
+		return strings.Contains(l, " 366 ")
+	})
+	assertContains(
+		t, aliceNames, " 353 ",
+		"RPL_NAMREPLY",
+	)
+	assertContains(
+		t, aliceNames, " 366 ",
+		"RPL_ENDOFNAMES",
+	)
+
+	// Both nicks should appear in the name list.
+	foundBothNames := false
+	for _, line := range aliceNames {
+		if strings.Contains(line, " 353 ") &&
+			strings.Contains(line, "alice") &&
+			strings.Contains(line, "bob") {
+			foundBothNames = true
+
+			break
+		}
+	}
+
+	if !foundBothNames {
+		t.Error("NAMES reply should list both alice and bob")
+	}
+
+	// ── LIST ──────────────────────────────────────────
+
+	alice.send("LIST")
+
+	aliceList := alice.readUntil(func(l string) bool {
+		return strings.Contains(l, " 323 ")
+	})
+	assertContains(
+		t, aliceList, " 322 ",
+		"RPL_LIST entry",
+	)
+	assertContains(
+		t, aliceList, "#integration",
+		"LIST includes #integration",
+	)
+	assertContains(
+		t, aliceList, " 323 ", //nolint:misspell // IRC RPL_LISTEND
+		"RPL_LISTEND", //nolint:misspell // IRC term
+	)
+
+	// ── WHO ───────────────────────────────────────────
+
+	bob.send("WHO #integration")
+
+	bobWho := bob.readUntil(func(l string) bool {
+		return strings.Contains(l, " 315 ")
+	})
+	assertContains(
+		t, bobWho, " 352 ",
+		"RPL_WHOREPLY",
+	)
+	assertContains(
+		t, bobWho, " 315 ",
+		"RPL_ENDOFWHO",
+	)
+
+	// ── WHOIS ─────────────────────────────────────────
+
+	alice.send("WHOIS bob")
+
+	aliceWhois := alice.readUntil(func(l string) bool {
+		return strings.Contains(l, " 318 ")
+	})
+	assertContains(
+		t, aliceWhois, " 311 ",
+		"RPL_WHOISUSER",
+	)
+	assertContains(
+		t, aliceWhois, " 312 ",
+		"RPL_WHOISSERVER",
+	)
+	assertContains(
+		t, aliceWhois, " 318 ",
+		"RPL_ENDOFWHOIS",
+	)
+
+	// ── WHOIS with channels ───────────────────────────
+
+	bob.send("WHOIS alice")
+
+	bobWhois := bob.readUntil(func(l string) bool {
+		return strings.Contains(l, " 318 ")
+	})
+	assertContains(
+		t, bobWhois, " 319 ",
+		"RPL_WHOISCHANNELS",
+	)
+	assertContains(
+		t, bobWhois, "#integration",
+		"WHOIS shows #integration channel",
+	)
+
+	// ── LUSERS ────────────────────────────────────────
+
+	alice.send("LUSERS")
+
+	aliceLusers := alice.readUntil(func(l string) bool {
+		return strings.Contains(l, " 255 ")
+	})
+	assertContains(
+		t, aliceLusers, " 251 ",
+		"RPL_LUSERCLIENT",
+	)
+	assertContains(
+		t, aliceLusers, " 255 ",
+		"RPL_LUSERME",
+	)
+
+	// ── NICK change ───────────────────────────────────
+
+	bob.send("NICK bobby")
+
+	bobNick := bob.readUntil(func(l string) bool {
+		return strings.Contains(l, "NICK") &&
+			strings.Contains(l, "bobby")
+	})
+	assertContains(
+		t, bobNick, "bobby",
+		"bob sees NICK change to bobby",
+	)
+
+	// alice should see the nick change relayed.
+	aliceNick := alice.readUntil(func(l string) bool {
+		return strings.Contains(l, "bobby")
+	})
+	assertContains(
+		t, aliceNick, "NICK",
+		"alice sees NICK command",
+	)
+	assertContains(
+		t, aliceNick, "bobby",
+		"alice sees new nick bobby",
+	)
+
+	// Change it back for remaining tests.
+	bob.send("NICK bob")
+	bob.readUntil(func(l string) bool {
+		return strings.Contains(l, "bob")
+	})
+	alice.readUntil(func(l string) bool {
+		return strings.Contains(l, "NICK") &&
+			strings.Contains(l, "bob")
+	})
+
+	// ── Duplicate NICK ────────────────────────────────
+
+	bob.send("NICK alice")
+
+	bobDupNick := bob.readUntil(func(l string) bool {
+		return strings.Contains(l, " 433 ")
+	})
+	assertContains(
+		t, bobDupNick, " 433 ",
+		"ERR_NICKNAMEINUSE",
+	)
+
+	// ── KICK ──────────────────────────────────────────
+	// alice is op; she kicks bob.
+
+	alice.send("KICK #integration bob :testing kick")
+
+	aliceKick := alice.readUntil(func(l string) bool {
+		return strings.Contains(l, "KICK")
+	})
+	assertContains(
+		t, aliceKick, "KICK",
+		"alice sees KICK echo",
+	)
+	assertContains(
+		t, aliceKick, "bob",
+		"KICK mentions bob",
+	)
+
+	bobKick := bob.readUntil(func(l string) bool {
+		return strings.Contains(l, "KICK")
+	})
+	assertContains(
+		t, bobKick, "KICK",
+		"bob receives KICK",
+	)
+	assertContains(
+		t, bobKick, "testing kick",
+		"KICK reason is relayed",
+	)
+
+	// bob rejoins.
+	bob.joinAndDrain("#integration")
+
+	// Drain alice's view of the rejoin.
+	alice.readUntil(func(l string) bool {
+		return strings.Contains(l, "JOIN") &&
+			strings.Contains(l, "bob")
+	})
+
+	// ── KICK non-op should fail ───────────────────────
+
+	bob.send("KICK #integration alice :nope")
+
+	bobKickFail := bob.readUntil(func(l string) bool {
+		return strings.Contains(l, " 482 ")
+	})
+	assertContains(
+		t, bobKickFail, " 482 ",
+		"ERR_CHANOPRIVSNEEDED",
+	)
+
+	// ── TOPIC lock (+t default) ───────────────────────
+	// +t is default, so bob should not be able to set
+	// topic.
+
+	bob.send("TOPIC #integration :bob tries topic")
+
+	bobTopicFail := bob.readUntil(func(l string) bool {
+		return strings.Contains(l, " 482 ")
+	})
+	assertContains(
+		t, bobTopicFail, " 482 ",
+		"ERR_CHANOPRIVSNEEDED for topic",
+	)
+
+	// ── PING / PONG ───────────────────────────────────
+
+	alice.send("PING :testtoken")
+
+	alicePong := alice.readUntil(func(l string) bool {
+		return strings.Contains(l, "PONG")
+	})
+	assertContains(
+		t, alicePong, "PONG",
+		"PONG response received",
+	)
+
+	// ── Unknown command ───────────────────────────────
+
+	bob.send("FOOBAR")
+
+	bobUnknown := bob.readUntil(func(l string) bool {
+		return strings.Contains(l, " 421 ")
+	})
+	assertContains(
+		t, bobUnknown, " 421 ",
+		"ERR_UNKNOWNCOMMAND",
+	)
+
+	// ── MOTD ──────────────────────────────────────────
+
+	alice.send("MOTD")
+
+	aliceMOTD := alice.readUntil(func(l string) bool {
+		return strings.Contains(l, " 376 ")
+	})
+	assertContains(
+		t, aliceMOTD, " 376 ",
+		"RPL_ENDOFMOTD",
+	)
+
+	// ── AWAY (set, check via DM, clear) ───────────────
+
+	alice.send("AWAY :gone fishing")
+
+	aliceAway := alice.readUntil(func(l string) bool {
+		return strings.Contains(l, " 306 ")
+	})
+	assertContains(
+		t, aliceAway, " 306 ",
+		"RPL_NOWAWAY",
+	)
+
+	// bob DMs alice — should get RPL_AWAY.
+	bob.send("PRIVMSG alice :are you there?")
+
+	bobAwayReply := bob.readUntil(func(l string) bool {
+		return strings.Contains(l, " 301 ")
+	})
+	assertContains(
+		t, bobAwayReply, " 301 ",
+		"RPL_AWAY for bob when messaging alice",
+	)
+	assertContains(
+		t, bobAwayReply, "gone fishing",
+		"away message relayed",
+	)
+
+	// Clear away.
+	alice.send("AWAY")
+	alice.readUntil(func(l string) bool {
+		return strings.Contains(l, " 305 ")
+	})
+
+	// ── PASS (set password post-registration) ─────────
+
+	alice.send("PASS :mypassword123")
+
+	alicePass := alice.readUntil(func(l string) bool {
+		return strings.Contains(l, "Password set")
+	})
+	assertContains(
+		t, alicePass, "Password set",
+		"password set confirmation",
+	)
+
+	// ── MODE -t/+t topic lock toggle ──────────────────
+
+	alice.send("MODE #integration -t")
+	alice.readUntil(func(l string) bool {
+		return strings.Contains(l, "-t")
+	})
+	bob.readUntil(func(l string) bool {
+		return strings.Contains(l, "-t")
+	})
+
+	// Now bob should be able to set topic.
+	bob.send("TOPIC #integration :bob sets topic now")
+
+	bobTopicOK := bob.readUntil(func(l string) bool {
+		return strings.Contains(l, "bob sets topic now")
+	})
+	assertContains(
+		t, bobTopicOK, "bob sets topic now",
+		"bob can set topic after -t",
+	)
+
+	// alice sees the topic change.
+	aliceTopicRelay := alice.readUntil(func(l string) bool {
+		return strings.Contains(l, "bob sets topic now")
+	})
+	assertContains(
+		t, aliceTopicRelay, "bob sets topic now",
+		"alice sees bob's topic after -t",
+	)
+
+	// Restore +t.
+	alice.send("MODE #integration +t")
+	alice.readUntil(func(l string) bool {
+		return strings.Contains(l, "+t")
+	})
+	bob.readUntil(func(l string) bool {
+		return strings.Contains(l, "+t")
+	})
+
+	// ── DM to nonexistent nick ────────────────────────
+
+	alice.send("PRIVMSG nobody123 :hello")
+
+	aliceNoSuch := alice.readUntil(func(l string) bool {
+		return strings.Contains(l, " 401 ")
+	})
+	assertContains(
+		t, aliceNoSuch, " 401 ",
+		"ERR_NOSUCHNICK",
+	)
+
+	// ── PART with reason ──────────────────────────────
+
+	bob.send("PART #integration :bye for now")
+
+	bobPart := bob.readUntil(func(l string) bool {
+		return strings.Contains(l, "PART")
+	})
+	assertContains(
+		t, bobPart, "PART",
+		"bob sees PART echo",
+	)
+
+	// alice sees bob PART via relay.
+	alicePart := alice.readUntil(func(l string) bool {
+		return strings.Contains(l, "PART") &&
+			strings.Contains(l, "bob")
+	})
+	assertContains(
+		t, alicePart, "bob",
+		"alice sees bob's PART",
+	)
+	assertContains(
+		t, alicePart, "bye for now",
+		"PART reason is relayed",
+	)
+
+	// bob rejoins for remaining tests.
+	bob.joinAndDrain("#integration")
+	alice.readUntil(func(l string) bool {
+		return strings.Contains(l, "JOIN") &&
+			strings.Contains(l, "bob")
+	})
+
+	// ── PART non-existent channel ─────────────────────
+
+	bob.send("PART #nonexistent")
+
+	bobPartFail := bob.readUntil(func(l string) bool {
+		return strings.Contains(l, " 403 ") ||
+			strings.Contains(l, " 442 ")
+	})
+
+	foundPartErr := false
+	for _, line := range bobPartFail {
+		if strings.Contains(line, " 403 ") ||
+			strings.Contains(line, " 442 ") {
+			foundPartErr = true
+
+			break
+		}
+	}
+
+	if !foundPartErr {
+		t.Error(
+			"expected ERR_NOSUCHCHANNEL or " +
+				"ERR_NOTONCHANNEL",
+		)
+	}
+
+	// ── User MODE query ───────────────────────────────
+
+	alice.send("MODE alice")
+
+	aliceUMode := alice.readUntil(func(l string) bool {
+		return strings.Contains(l, " 221 ")
+	})
+	assertContains(
+		t, aliceUMode, " 221 ",
+		"RPL_UMODEIS",
+	)
+
+	// ── Multiple channel operation ────────────────────
+
+	alice.send("JOIN #second")
+	alice.readUntil(func(l string) bool {
+		return strings.Contains(l, " 366 ")
+	})
+
+	bob.send("JOIN #second")
+	bob.readUntil(func(l string) bool {
+		return strings.Contains(l, " 366 ")
+	})
+
+	// Drain alice seeing bob join.
+	alice.readUntil(func(l string) bool {
+		return strings.Contains(l, "JOIN") &&
+			strings.Contains(l, "bob")
+	})
+
+	alice.send("PRIVMSG #second :cross-channel test")
+
+	bobCross := bob.readUntil(func(l string) bool {
+		return strings.Contains(l, "cross-channel test")
+	})
+	assertContains(
+		t, bobCross, "cross-channel test",
+		"bob receives message in #second",
+	)
+
+	// Clean up #second.
+	alice.send("PART #second")
+	alice.readUntil(func(l string) bool {
+		return strings.Contains(l, "PART")
+	})
+	bob.send("PART #second")
+	bob.readUntil(func(l string) bool {
+		return strings.Contains(l, "PART")
+	})
+
+	// ── QUIT ──────────────────────────────────────────
+
+	bob.send("QUIT :integration test done")
+
+	bobQuit := bob.readUntil(func(l string) bool {
+		return strings.Contains(l, "ERROR")
+	})
+	assertContains(
+		t, bobQuit, "integration test done",
+		"QUIT reason echoed",
+	)
+
+	// alice should see bob's QUIT via relay.
+	aliceQuit := alice.readUntil(func(l string) bool {
+		return strings.Contains(l, "QUIT") &&
+			strings.Contains(l, "bob")
+	})
+	assertContains(
+		t, aliceQuit, "bob",
+		"alice sees bob's QUIT",
+	)
+}
+
+// TestIntegrationModeSecret tests +s (secret) channel
+// mode — verifies that +s can be set and the mode is
+// reflected in MODE queries.
+func TestIntegrationModeSecret(t *testing.T) {
+	t.Parallel()
+
+	env := newTestEnv(t)
+
+	alice := env.dial(t)
+	alice.register("alice")
+
+	alice.joinAndDrain("#secretroom")
+
+	// Set +s.
+	alice.send("MODE #secretroom +s")
+	aliceLines := alice.readUntil(func(l string) bool {
+		return strings.Contains(l, "+s")
+	})
+	assertContains(
+		t, aliceLines, "+s",
+		"alice sees MODE +s confirmation",
+	)
+
+	// Verify mode is reflected in query.
+	alice.send("MODE #secretroom")
+	modeLines := alice.readUntil(func(l string) bool {
+		return strings.Contains(l, " 324 ")
+	})
+	assertContains(
+		t, modeLines, "s",
+		"channel mode includes s",
+	)
+}
+
+// TestIntegrationModeModerated tests +m (moderated) mode
+// — non-voiced users cannot send.
+func TestIntegrationModeModerated(t *testing.T) {
+	t.Parallel()
+
+	env := newTestEnv(t)
+
+	alice := env.dial(t)
+	alice.register("alice")
+
+	bob := env.dial(t)
+	bob.register("bob")
+
+	alice.joinAndDrain("#modtest")
+	bob.joinAndDrain("#modtest")
+
+	// Drain alice's view of bob's join.
+	alice.readUntil(func(l string) bool {
+		return strings.Contains(l, "JOIN") &&
+			strings.Contains(l, "bob")
+	})
+
+	// Set +m.
+	alice.send("MODE #modtest +m")
+	alice.readUntil(func(l string) bool {
+		return strings.Contains(l, "+m")
+	})
+	bob.readUntil(func(l string) bool {
+		return strings.Contains(l, "+m")
+	})
+
+	// bob should get an error trying to send.
+	bob.send("PRIVMSG #modtest :should fail")
+	bobLines := bob.readUntil(func(l string) bool {
+		return strings.Contains(l, " 404 ") ||
+			strings.Contains(l, " 482 ")
+	})
+
+	foundModErr := false
+	for _, line := range bobLines {
+		if strings.Contains(line, " 404 ") ||
+			strings.Contains(line, " 482 ") {
+			foundModErr = true
+
+			break
+		}
+	}
+
+	if !foundModErr {
+		t.Error(
+			"non-voiced user should not be able to send " +
+				"in +m channel",
+		)
+	}
+
+	// Grant +v to bob, then he should be able to send.
+	alice.send("MODE #modtest +v bob")
+	alice.readUntil(func(l string) bool {
+		return strings.Contains(l, "+v")
+	})
+	bob.readUntil(func(l string) bool {
+		return strings.Contains(l, "+v")
+	})
+
+	bob.send("PRIVMSG #modtest :voiced message")
+	aliceLines := alice.readUntil(func(l string) bool {
+		return strings.Contains(l, "voiced message")
+	})
+	assertContains(
+		t, aliceLines, "voiced message",
+		"alice receives voiced bob's message",
+	)
+}
+
+// TestIntegrationThirdClientObserver verifies that a third
+// client observing the same channel receives messages from
+// the other two.
+func TestIntegrationThirdClientObserver(t *testing.T) {
+	t.Parallel()
+
+	env := newTestEnv(t)
+
+	alice := env.dial(t)
+	alice.register("alice")
+
+	bob := env.dial(t)
+	bob.register("bob")
+
+	carol := env.dial(t)
+	carol.register("carol")
+
+	alice.joinAndDrain("#trio")
+	bob.joinAndDrain("#trio")
+	carol.joinAndDrain("#trio")
+
+	// Drain join notifications.
+	time.Sleep(100 * time.Millisecond)
+
+	// alice sends; both bob and carol should receive.
+	alice.send("PRIVMSG #trio :hello trio")
+
+	bobLines := bob.readUntil(func(l string) bool {
+		return strings.Contains(l, "hello trio")
+	})
+	assertContains(
+		t, bobLines, "hello trio",
+		"bob receives trio message",
+	)
+
+	carolLines := carol.readUntil(func(l string) bool {
+		return strings.Contains(l, "hello trio")
+	})
+	assertContains(
+		t, carolLines, "hello trio",
+		"carol receives trio message",
+	)
+}