diff --git a/go/net/tinylb/tinylb_test.go b/go/net/tinylb/tinylb_test.go
new file mode 100644
index 0000000..acf2dda
--- /dev/null
+++ b/go/net/tinylb/tinylb_test.go
@@ -0,0 +1,230 @@
+package tinylb
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"net"
+	"strings"
+	"testing"
+	"time"
+
+	"source.monogon.dev/metropolis/pkg/event/memory"
+	"source.monogon.dev/metropolis/pkg/supervisor"
+)
+
+func TestLoadbalancer(t *testing.T) {
+	v := memory.Value[BackendSet]{}
+	set := BackendSet{}
+	v.Set(set.Clone())
+
+	ln, err := net.Listen("tcp", ":0")
+	if err != nil {
+		t.Fatalf("Listen failed: %v", err)
+	}
+	s := Server{
+		Provider: &v,
+		Listener: ln,
+	}
+	supervisor.TestHarness(t, s.Run)
+
+	connect := func() net.Conn {
+		conn, err := net.Dial("tcp", ln.Addr().String())
+		if err != nil {
+			t.Fatalf("Connection failed: %v", err)
+		}
+		return conn
+	}
+
+	c := connect()
+	buf := make([]byte, 128)
+	if _, err := c.Read(buf); err == nil {
+		t.Fatalf("Expected error on read (no backends yet)")
+	}
+
+	// Now add a backend and expect it to be served.
+	makeBackend := func(hello string) net.Listener {
+		aln, err := net.Listen("tcp", ":0")
+		if err != nil {
+			t.Fatalf("Failed to make backend listener: %v", err)
+		}
+		// Start backend.
+		go func() {
+			for {
+				c, err := aln.Accept()
+				if err != nil {
+					return
+				}
+				// For each connection, keep writing 'hello' over and over, newline-separated.
+				go func() {
+					defer c.Close()
+					for {
+						if _, err := fmt.Fprintf(c, "%s\n", hello); err != nil {
+							return
+						}
+						time.Sleep(100 * time.Millisecond)
+					}
+				}()
+			}
+		}()
+		addr := aln.Addr().(*net.TCPAddr)
+		set.Insert(hello, &SimpleTCPBackend{Remote: addr.AddrPort().String()})
+		v.Set(set.Clone())
+		return aln
+	}
+
+	as1 := makeBackend("a")
+	defer as1.Close()
+
+	for {
+		c = connect()
+		_, err := c.Read(buf)
+		c.Close()
+		if err == nil {
+			break
+		}
+	}
+
+	measure := func() map[string]int {
+		res := make(map[string]int)
+		for {
+			count := 0
+			for _, v := range res {
+				count += v
+			}
+			if count >= 20 {
+				return res
+			}
+
+			c := connect()
+			b := bufio.NewScanner(c)
+			if !b.Scan() {
+				err := b.Err()
+				if err == nil {
+					err = io.EOF
+				}
+				t.Fatalf("Scan failed: %v", err)
+			}
+			v := b.Text()
+			res[v]++
+			c.Close()
+		}
+	}
+
+	m := measure()
+	if m["a"] < 20 {
+		t.Errorf("Expected only one backend, got: %v", m)
+	}
+
+	as2 := makeBackend("b")
+	defer as2.Close()
+
+	as3 := makeBackend("c")
+	defer as3.Close()
+
+	as4 := makeBackend("d")
+	defer as4.Close()
+
+	m = measure()
+	for _, id := range []string{"a", "b", "c", "d"} {
+		if want, got := 4, m[id]; got < want {
+			t.Errorf("Expected at least %d responses from %s, got %d", want, id, got)
+		}
+	}
+
+	// Test killing backend connections on backend removal.
+	// Open a bunch of connections to 'a'.
+	var conns []*bufio.Scanner
+	for len(conns) < 5 {
+		c := connect()
+		b := bufio.NewScanner(c)
+		b.Scan()
+		if b.Text() != "a" {
+			c.Close()
+		} else {
+			conns = append(conns, b)
+		}
+	}
+
+	// Now remove the 'a' backend.
+	set.Delete("a")
+	v.Set(set.Clone())
+	// All open connections should now get killed.
+	for _, b := range conns {
+		start := time.Now().Add(time.Second)
+		for b.Scan() {
+			if time.Now().After(start) {
+				t.Errorf("Connection still alive")
+				break
+			}
+		}
+	}
+}
+
+func BenchmarkLB(b *testing.B) {
+	v := memory.Value[BackendSet]{}
+	set := BackendSet{}
+	v.Set(set.Clone())
+
+	ln, err := net.Listen("tcp", ":0")
+	if err != nil {
+		b.Fatalf("Listen failed: %v", err)
+	}
+	s := Server{
+		Provider: &v,
+		Listener: ln,
+	}
+	supervisor.TestHarness(b, s.Run)
+
+	makeBackend := func(hello string) net.Listener {
+		aln, err := net.Listen("tcp", ":0")
+		if err != nil {
+			b.Fatalf("Failed to make backend listener: %v", err)
+		}
+		// Start backend.
+		go func() {
+			for {
+				c, err := aln.Accept()
+				if err != nil {
+					return
+				}
+				go func() {
+					fmt.Fprintf(c, "%s\n", hello)
+					c.Close()
+				}()
+			}
+		}()
+		addr := aln.Addr().(*net.TCPAddr)
+		set.Insert(hello, &SimpleTCPBackend{Remote: addr.AddrPort().String()})
+		v.Set(set.Clone())
+		return aln
+	}
+	var backends []net.Listener
+	for i := 0; i < 10; i++ {
+		b := makeBackend(fmt.Sprintf("backend%d", i))
+		backends = append(backends, b)
+	}
+
+	defer func() {
+		for _, b := range backends {
+			b.Close()
+		}
+	}()
+
+	b.ResetTimer()
+	b.RunParallel(func(pb *testing.PB) {
+		for pb.Next() {
+			conn, err := net.Dial("tcp", ln.Addr().String())
+			if err != nil {
+				b.Fatalf("Connection failed: %v", err)
+			}
+			buf := bufio.NewScanner(conn)
+			buf.Scan()
+			if !strings.HasPrefix(buf.Text(), "backend") {
+				b.Fatalf("Invalid backend response: %q", buf.Text())
+			}
+			conn.Close()
+		}
+	})
+	b.StopTimer()
+}