You need to put the class where the constructor is called into the @PrepareForTest annotation instead of the class which is being constructed – see Mock construction of new objects.
In your case:
✗ @PrepareForTest(MyQueryClass.class)
✓ @PrepareForTest(A.class)
More general:
✗ @PrepareForTest(NewInstanceClass.class)
✓ @PrepareForTest(ClassThatCreatesTheNewInstance.class)