xmllite/tests: Use an iface instead of a vtbl pointer in testinput.

dlls/xmllite/tests/reader.c

@@ -19,6 +19,7 @@
  */
 
 #define COBJMACROS
+#define CONST_VTABLE
 
 #include <stdarg.h>
 #include <stdio.h>
@@ -258,13 +259,13 @@ static void test_read_state_(IXmlReader *reader, XmlReadState expected,
 
 typedef struct _testinput
 {
-    const IUnknownVtbl *lpVtbl;
+    IUnknown IUnknown_iface;
     LONG ref;
 } testinput;
 
 static inline testinput *impl_from_IUnknown(IUnknown *iface)
 {
-    return (testinput *)((char*)iface - FIELD_OFFSET(testinput, lpVtbl));
+    return CONTAINING_RECORD(iface, testinput, IUnknown_iface);
 }
 
 static HRESULT WINAPI testinput_QueryInterface(IUnknown *iface, REFIID riid, void** ppvObj)
@@ -317,10 +318,10 @@ static HRESULT testinput_createinstance(void **ppObj)
     input = HeapAlloc(GetProcessHeap(), 0, sizeof (*input));
     if(!input) return E_OUTOFMEMORY;
 
-    input->lpVtbl = &testinput_vtbl;
+    input->IUnknown_iface.lpVtbl = &testinput_vtbl;
     input->ref = 1;
 
-    *ppObj = &input->lpVtbl;
+    *ppObj = &input->IUnknown_iface;
 
     return S_OK;
 }
@@ -372,13 +373,14 @@ static void test_reader_create(void)
     hr = testinput_createinstance((void**)&input);
     ok(hr == S_OK, "Expected S_OK, got %08x\n", hr);
 
+    if (hr == S_OK)
+    {
         input_iids.count = 0;
         hr = IXmlReader_SetInput(reader, input);
         ok(hr == E_NOINTERFACE, "Expected E_NOINTERFACE, got %08x\n", hr);
         ok_iids(&input_iids, setinput_full, setinput_full_old, FALSE);
-
         IUnknown_Release(input);
-
+    }
     IXmlReader_Release(reader);
 }