raspi: increase test coverage

Signed-off-by: deadprogram <ron@hybridgroup.com>

platforms/raspi/pwm_pin_test.go

@@ -1,6 +1,7 @@
 package raspi
 
 import (
+	"errors"
 	"testing"
 
 	"gobot.io/x/gobot/gobottest"
@@ -33,6 +34,10 @@ func TestPwmPin(t *testing.T) {
 	dc, _ = pin.DutyCycle()
 	gobottest.Assert(t, dc, uint32(10000))
 
+	gobottest.Assert(t, pin.SetDutyCycle(999999999), errors.New("Duty cycle exceeds period."))
+	dc, _ = pin.DutyCycle()
+	gobottest.Assert(t, dc, uint32(10000))
+
 	// call currently fails in test
 	gobottest.Refute(t, pin.Unexport(), nil)
 }

platforms/raspi/raspi_adaptor_test.go

@@ -147,6 +147,10 @@ func TestAdaptorDigitalIO(t *testing.T) {
 	fs.WithReadError = true
 	_, err := a.DigitalRead("13")
 	gobottest.Assert(t, err, errors.New("read error"))
+
+	fs.WithWriteError = true
+	_, err = a.DigitalRead("7")
+	gobottest.Assert(t, err, errors.New("write error"))
 }
 
 func TestAdaptorI2c(t *testing.T) {