hwmonio:: Add Interface base class and tests

Enable injecting hwmonio::HwmonIO mocks for testing.

Tested: Ran on quanta-q71l and saw all sensors exported to dbus as
expected with the expected values.

Change-Id: I35912bf2a733932d9e1e774ff53b0114ae16560b
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/test/Makefile.am b/test/Makefile.am
index 7f302ca..1b07171 100644
--- a/test/Makefile.am
+++ b/test/Makefile.am
@@ -12,9 +12,11 @@
 	$(PHOSPHOR_DBUS_INTERFACES_LIBS)
 
 # Run all 'check' test programs
-check_PROGRAMS = hwmon_unittest
+check_PROGRAMS = hwmon_unittest fanpwm_unittest
 TESTS = $(check_PROGRAMS)
 
 hwmon_unittest_SOURCES = hwmon_unittest.cpp
 hwmon_unittest_LDADD = $(top_builddir)/hwmon.o
 
+fanpwm_unittest_SOURCES = fanpwm_unittest.cpp
+fanpwm_unittest_LDADD = $(PHOSPHOR_LOGGING_LIBS) $(top_builddir)/fan_pwm.o