Detect if CUnit is installed

Makefile

@@ -26,9 +26,12 @@ bin/%.o: src/%.c | init
 docs:
 	@printf "not implemented yet.\n" >&2
 
-test: bin/libgargoyle.so bin/gargoyle-test
+test: cunit bin/libgargoyle.so bin/gargoyle-test
 	bin/gargoyle-test
 
+cunit:
+	if pkg-config cunit; then printf 'CUnit is installed\n'; else printf 'please install CUnit\n' >&2; exit 1; fi
+
 bin/gargoyle-test: $(addprefix bin/test/,$(addsuffix .o,$(GARGOYLE_TEST_OBJS)))
 	cc $(LDFLAGS) -L bin -o $@ $^ -l gargoyle -l cunit -l m