Add Google Test submodule

.gitmodules

@@ -7,3 +7,6 @@
 [submodule "lib/ugfx"]
 	path = lib/ugfx
 	url = https://bitbucket.org/Tectu/ugfx
+[submodule "lib/googletest"]
+	path = lib/googletest
+	url = https://github.com/google/googletest

lib/googletest

@@ -0,0 +1 @@
+Subproject commit ec44c6c1675c25b9827aacd08c02433cccde7780