test: add comprehensive test suite

- Integration tests for all API endpoints (session, state, channels, messages)
- Tests for all commands: PRIVMSG, JOIN, PART, NICK, TOPIC, QUIT, PING
- Edge cases: duplicate nick, empty/invalid inputs, malformed JSON, bad auth
- Long-poll tests: delivery on notify and timeout behavior
- DM tests: delivery to recipient, echo to sender, nonexistent user
- Ephemeral channel cleanup test
- Concurrent session creation test
- Nick broadcast to channel members test
- DB unit tests: all CRUD operations, message queue, history
- Broker unit tests: wait/notify, remove, concurrent access

internal/broker/broker_test.go

@@ -0,0 +1,94 @@
+package broker
+
+import (
+	"sync"
+	"testing"
+	"time"
+)
+
+func TestNewBroker(t *testing.T) {
+	b := New()
+	if b == nil {
+		t.Fatal("expected non-nil broker")
+	}
+}
+
+func TestWaitAndNotify(t *testing.T) {
+	b := New()
+	ch := b.Wait(1)
+
+	go func() {
+		time.Sleep(10 * time.Millisecond)
+		b.Notify(1)
+	}()
+
+	select {
+	case <-ch:
+	case <-time.After(2 * time.Second):
+		t.Fatal("timeout")
+	}
+}
+
+func TestNotifyWithoutWaiters(t *testing.T) {
+	b := New()
+	b.Notify(42) // should not panic
+}
+
+func TestRemove(t *testing.T) {
+	b := New()
+	ch := b.Wait(1)
+	b.Remove(1, ch)
+
+	b.Notify(1)
+	select {
+	case <-ch:
+		t.Fatal("should not receive after remove")
+	case <-time.After(50 * time.Millisecond):
+	}
+}
+
+func TestMultipleWaiters(t *testing.T) {
+	b := New()
+	ch1 := b.Wait(1)
+	ch2 := b.Wait(1)
+
+	b.Notify(1)
+
+	select {
+	case <-ch1:
+	case <-time.After(time.Second):
+		t.Fatal("ch1 timeout")
+	}
+	select {
+	case <-ch2:
+	case <-time.After(time.Second):
+		t.Fatal("ch2 timeout")
+	}
+}
+
+func TestConcurrentWaitNotify(t *testing.T) {
+	b := New()
+	var wg sync.WaitGroup
+
+	for i := 0; i < 100; i++ {
+		wg.Add(1)
+		go func(uid int64) {
+			defer wg.Done()
+			ch := b.Wait(uid)
+			b.Notify(uid)
+			select {
+			case <-ch:
+			case <-time.After(time.Second):
+				t.Error("timeout")
+			}
+		}(int64(i % 10))
+	}
+
+	wg.Wait()
+}
+
+func TestRemoveNonexistent(t *testing.T) {
+	b := New()
+	ch := make(chan struct{}, 1)
+	b.Remove(999, ch) // should not panic
+}