DI: allow to trigger the lazy instantiation of a mock service instance directly

Basically the mocking mechanism just switches the configuration
and then waits for the service to be accessed in order to cause acutual
instantiation of the mock service implementation. But sometimes we want
to prepare and rig the mock instance prior to the first invocation;
in such cases it can be handy just to trigger the lazy creating process

src/lib/depend-inject.hpp

@@ -324,17 +324,26 @@ namespace lib {
               return bool(mock_);
             }
           
+          /** trigger lazy service object instantiation */
+          MOC&
+          triggerCreate()
+            {
+              Depend<SRV>{}.operator()();
+              ENSURE (mock_);
+              return *mock_;
+            }
+          
           MOC&
           operator* ()  const
             {
-              ENSURE (mock_);
+              REQUIRE (mock_);
               return *mock_;
             }
           
           MOC*
           operator-> ()  const
             {
-              ENSURE (mock_);
+              REQUIRE (mock_);
               return mock_.get();
             }
         };

tests/gui/ctrl/element-access-test.cpp

@@ -116,6 +116,7 @@ namespace test {
           auto location = UICoord{"win-1","persp-A","thePanel","someView","tab#5"};
           DummyTab dummyTab;
           
+          fakeDirectory.triggerCreate();
           fakeDirectory->expectedQuery = location;
           fakeDirectory->expectedAnswer = &dummyTab;