tests: Add basic unit test based on virtual_image device

meson.build

@@ -140,6 +140,11 @@ if get_option('gtk-examples')
     subdir('demo')
 endif
 
+# The tests require introspeciton support to run
+if get_option('introspection')
+    subdir('tests')
+endif
+
 pkgconfig = import('pkgconfig')
 pkgconfig.generate(
   name: 'libfprint',