SdBusError: Add test cases

This adds basic unit testing to the SdBusError class so we have full
coverage of all the functionality.

Tested:
    Ran through the unit test suite including the changes that build
    valgrind runs and code coverage suppport.

Change-Id: I6d3bdbd2e0332ae5372796cb2a380ccddbee10ec
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/test/Makefile.am b/test/Makefile.am
index 0c71949..442d084 100644
--- a/test/Makefile.am
+++ b/test/Makefile.am
@@ -24,6 +24,10 @@
 bus_match_SOURCES = bus/match.cpp
 bus_match_LDADD = $(gtest_ldadd)
 
+check_PROGRAMS += exception_sdbus_error
+exception_sdbus_error_SOURCES = exception/sdbus_error.cpp
+exception_sdbus_error_LDADD = $(gtest_ldadd)
+
 check_PROGRAMS += message_append
 message_append_SOURCES = message/append.cpp
 message_append_CXXFLAGS = $(legacy_test_cxxflags)