test: add tests of 'read' and 'write' shell commands

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
diff --git a/test/cmd/Makefile b/test/cmd/Makefile
index 2ffde87..7848f34 100644
--- a/test/cmd/Makefile
+++ b/test/cmd/Makefile
@@ -18,6 +18,7 @@
 obj-$(CONFIG_CMD_PWM) += pwm.o
 obj-$(CONFIG_CMD_SEAMA) += seama.o
 ifdef CONFIG_SANDBOX
+obj-$(CONFIG_CMD_READ) += rw.o
 obj-$(CONFIG_CMD_SETEXPR) += setexpr.o
 endif
 obj-$(CONFIG_CMD_TEMPERATURE) += temperature.o