tests: Add fp-device basic unit tests

Use the virtual image device as base for now, while the new setup allows
to create easily fake device drivers without including the driver in
libfprint itself and test all the fpi_device functionalities.

tests/test-utils.h

@@ -21,3 +21,17 @@
 
 void fpt_setup_virtual_device_environment (void);
 void fpt_teardown_virtual_device_environment (void);
+
+typedef struct _FptContext
+{
+  FpContext *fp_context;
+  FpDevice  *device;
+  gpointer   user_data;
+} FptContext;
+
+FptContext * fpt_context_new (void);
+FptContext * fpt_context_new_with_virtual_imgdev (void);
+
+void fpt_context_free (FptContext *test_context);
+
+G_DEFINE_AUTOPTR_CLEANUP_FUNC (FptContext, fpt_context_free)