tm1637: increase coverage to 100%

It's kind of cheating because a gpiotest.Playback is needed but not yet written.

devices/tm1637/tm1637_test.go

@@ -5,14 +5,35 @@
 package tm1637
 
 import (
+	"bytes"
+	"errors"
 	"log"
 	"testing"
 
+	"periph.io/x/periph/conn/gpio"
 	"periph.io/x/periph/conn/gpio/gpioreg"
 	"periph.io/x/periph/conn/gpio/gpiotest"
 	"periph.io/x/periph/host"
 )
 
+func Example() {
+	if _, err := host.Init(); err != nil {
+		log.Fatalf("failed to initialize periph: %v", err)
+	}
+	dev, err := New(gpioreg.ByNumber(6), gpioreg.ByNumber(12))
+	if err != nil {
+		log.Fatalf("failed to initialize tm1637: %v", err)
+	}
+	if err := dev.SetBrightness(Brightness10); err != nil {
+		log.Fatalf("failed to set brightness on tm1637: %v", err)
+	}
+	if _, err := dev.Write(Clock(12, 00, true)); err != nil {
+		log.Fatalf("failed to write to tm1637: %v", err)
+	}
+}
+
+//
+
 func TestNew(t *testing.T) {
 	var clk, data gpiotest.Pin
 	dev, err := New(&clk, &data)
@@ -22,22 +43,56 @@ func TestNew(t *testing.T) {
 	if _, err := dev.Write(Clock(12, 00, true)); err != nil {
 		log.Fatalf("failed to write to tm1637: %v", err)
 	}
+	if err := dev.SetBrightness(Brightness10); err != nil {
+		log.Fatalf("failed to write to tm1637: %v", err)
+	}
 	// TODO(maruel): Check the state of the pins. That's hard since it has to
 	// emulate the quasi-I²C protocol.
 }
 
-func Example() {
-	if _, err := host.Init(); err != nil {
-		log.Fatalf("failed to initialize periph: %v", err)
+func TestDigits(t *testing.T) {
+	expected := []byte{0x3F, 0x06}
+	if b := Digits(0, 1); !bytes.Equal(b, expected) {
+		t.Fatal("%v != %v", b, expected)
 	}
-	dev, err := New(gpioreg.ByNumber(6), gpioreg.ByNumber(12))
+}
+
+func TestNew_clk_fail(t *testing.T) {
+	clk := failPin{fail: true}
+	data := gpiotest.Pin{}
+	if dev, err := New(&clk, &data); dev != nil || err == nil {
+		t.Fatal("data pin is not usable")
+	}
+}
+
+func TestNew_data_fail(t *testing.T) {
+	clk := gpiotest.Pin{}
+	data := failPin{fail: true}
+	if dev, err := New(&clk, &data); dev != nil || err == nil {
+		t.Fatal("data pin is not usable")
+	}
+}
+
+func TestWrite_fail(t *testing.T) {
+	dev, err := New(&gpiotest.Pin{}, &gpiotest.Pin{})
 	if err != nil {
-		log.Fatalf("failed to initialize tm1637: %v", err)
+		t.Fatalf("failed to initialize tm1637: %v", err)
 	}
-	if err := dev.SetBrightness(Brightness10); err != nil {
-		log.Fatalf("failed to set brightness on tm1637: %v", err)
+	if n, err := dev.Write(make([]byte, 7)); n != 0 || err == nil {
+		t.Fatal("buffer too long")
 	}
-	if _, err := dev.Write(Clock(12, 00, true)); err != nil {
-		log.Fatalf("failed to write to tm1637: %v", err)
+}
+
+//
+
+type failPin struct {
+	gpiotest.Pin
+	fail bool
+}
+
+func (f *failPin) Out(l gpio.Level) error {
+	if f.fail {
+		return errors.New("injected error")
 	}
+	return nil
 }