diff --git a/internal/engine/experiment/smtp/smtp_test.go b/internal/engine/experiment/smtp/smtp_test.go
new file mode 100644
index 0000000..e49af52
--- /dev/null
+++ b/internal/engine/experiment/smtp/smtp_test.go
@@ -0,0 +1,185 @@
+package smtp
+
+import (
+	"bufio"
+	"context"
+	"crypto/tls"
+	"errors"
+	"fmt"
+	"net"
+	"strings"
+	"testing"
+
+	"github.com/ooni/probe-cli/v3/internal/engine/mockable"
+	"github.com/ooni/probe-cli/v3/internal/model"
+)
+
+func plaintextListener() net.Listener {
+	l, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		if l, err = net.Listen("tcp6", "[::1]:0"); err != nil {
+			panic(fmt.Sprintf("httptest: failed to listen on a port: %v", err))
+		}
+	}
+	return l
+}
+
+func tlsListener(l net.Listener) net.Listener {
+	return tls.NewListener(l, &tls.Config{})
+}
+
+func listener_addr(l net.Listener) string {
+	return l.Addr().String()
+}
+
+func ValidSMTPServer(conn net.Conn) {
+	for {
+		command, err := bufio.NewReader(conn).ReadString('\n')
+		if err != nil {
+			return
+		}
+
+		if command == "" {
+		} else if command == "NOOP" {
+			conn.Write([]byte("250 2.0.0 Ok\n"))
+		} else if command == "STARTTLS" {
+			conn.Write([]byte("220 2.0.0 Ready to start TLS\n"))
+			// TODO: conn.Close does not actually close connection? or does client not detect it?
+			conn.Close()
+			return
+		} else if strings.HasPrefix(command, "EHLO") {
+			conn.Write([]byte("250 mock.example.com\n"))
+		}
+		conn.Write([]byte("\n"))
+	}
+}
+
+func TCPServer(l net.Listener) {
+	for {
+		conn, err := l.Accept()
+		if err != nil {
+			continue
+		}
+		defer conn.Close()
+		conn.Write([]byte("220 mock.example.com ESMTP (spam is not appreciated)\n"))
+		ValidSMTPServer(conn)
+	}
+}
+
+func TestMeasurer_run(t *testing.T) {
+	// runHelper is an helper function to run this set of tests.
+	runHelper := func(input string) (*model.Measurement, model.ExperimentMeasurer, error) {
+		m := NewExperimentMeasurer(Config{})
+		if m.ExperimentName() != "smtp" {
+			t.Fatal("invalid experiment name")
+		}
+		if m.ExperimentVersion() != "0.0.1" {
+			t.Fatal("invalid experiment version")
+		}
+		ctx := context.Background()
+		meas := &model.Measurement{
+			Input: model.MeasurementTarget(input),
+		}
+		sess := &mockable.Session{
+			MockableLogger: model.DiscardLogger,
+		}
+		callbacks := model.NewPrinterCallbacks(model.DiscardLogger)
+		err := m.Run(ctx, sess, meas, callbacks)
+		return meas, m, err
+	}
+
+	t.Run("with empty input", func(t *testing.T) {
+		_, _, err := runHelper("")
+		if !errors.Is(err, errNoInputProvided) {
+			t.Fatal("unexpected error", err)
+		}
+	})
+
+	t.Run("with invalid URL", func(t *testing.T) {
+		_, _, err := runHelper("\t")
+		if !errors.Is(err, errInputIsNotAnURL) {
+			t.Fatal("unexpected error", err)
+		}
+	})
+
+	t.Run("with invalid scheme", func(t *testing.T) {
+		_, _, err := runHelper("https://8.8.8.8:443/")
+		if !errors.Is(err, errInvalidScheme) {
+			t.Fatal("unexpected error", err)
+		}
+	})
+
+	t.Run("with broken TLS", func(t *testing.T) {
+		p := plaintextListener()
+		defer p.Close()
+
+		l := tlsListener(p)
+		defer l.Close()
+		addr := listener_addr(l)
+		go TCPServer(l)
+
+		meas, m, err := runHelper("smtps://" + addr)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		tk := meas.TestKeys.(*TestKeys)
+
+		for _, run := range tk.Runs {
+			for _, handshake := range run.TLSHandshakes {
+				if *handshake.Failure != "unknown_failure: remote error: tls: unrecognized name" {
+					t.Fatal("expected unrecognized_name in TLS handshake")
+				}
+			}
+
+			if run.NoOpCounter != 0 {
+				t.Fatalf("expected to not have any noops, not %d noops", run.NoOpCounter)
+			}
+		}
+
+		ask, err := m.GetSummaryKeys(meas)
+		if err != nil {
+			t.Fatal("cannot obtain summary")
+		}
+		summary := ask.(SummaryKeys)
+		if summary.IsAnomaly {
+			t.Fatal("expected no anomaly")
+		}
+	})
+
+	t.Run("with broken starttls", func(t *testing.T) {
+		l := plaintextListener()
+		defer l.Close()
+		addr := listener_addr(l)
+
+		go TCPServer(l)
+
+		meas, m, err := runHelper("smtp://" + addr)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		tk := meas.TestKeys.(*TestKeys)
+
+		for _, run := range tk.Runs {
+			for _, handshake := range run.TLSHandshakes {
+				if *handshake.Failure != "generic_timeout_error" {
+					t.Fatal("expected timeout in TLS handshake")
+				}
+			}
+
+			if run.NoOpCounter != 0 {
+				t.Fatalf("expected to not have any noops, not %d noops", run.NoOpCounter)
+			}
+		}
+
+		ask, err := m.GetSummaryKeys(meas)
+		if err != nil {
+			t.Fatal("cannot obtain summary")
+		}
+		summary := ask.(SummaryKeys)
+		if summary.IsAnomaly {
+			t.Fatal("expected no anomaly")
+		}
+	})
+}