tester: add very basic mock structs for testing i2c devices, based on work done by @rogpeppe

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

tester/i2c.go

@@ -0,0 +1,52 @@
+package tester
+
+import (
+	qt "github.com/frankban/quicktest"
+)
+
+// I2CBus implements the I2C interface in memory for testing.
+type I2CBus struct {
+	C       *qt.C
+	Devices []*I2CDevice
+}
+
+// NewI2CBus returns an I2CBus mock I2C instance that uses c to flag errors
+// if they happen. After creating a I2C instance, add devices
+// to it with addDevice before using NewI2CBus interface.
+func NewI2CBus(c *qt.C) *I2CBus {
+	return &I2CBus{
+		C: c,
+	}
+}
+
+// AddDevice adds a new mock device to the mock I2C bus.
+func (bus *I2CBus) AddDevice(d *I2CDevice) {
+	bus.Devices = append(bus.Devices, d)
+}
+
+// ReadRegister implements I2C.ReadRegister.
+func (bus *I2CBus) ReadRegister(addr uint8, r uint8, buf []byte) error {
+	return bus.FindDevice(addr).ReadRegister(r, buf)
+}
+
+// WriteRegister implements I2C.WriteRegister.
+func (bus *I2CBus) WriteRegister(addr uint8, r uint8, buf []byte) error {
+	return bus.FindDevice(addr).WriteRegister(r, buf)
+}
+
+// Tx implements I2C.Tx.
+func (bus *I2CBus) Tx(addr uint16, input, output []byte) error {
+	// TODO: implement this
+	return nil
+}
+
+// FindDevice returns the device with the given address.
+func (bus *I2CBus) FindDevice(addr uint8) *I2CDevice {
+	for _, dev := range bus.Devices {
+		if dev.Addr == addr {
+			return dev
+		}
+	}
+	bus.C.Fatalf("invalid device addr %#x passed to i2c bus", addr)
+	panic("unreachable")
+}