We want to be sure that `Library` actually exists when we modify it.
While it is not a silver bullet (user can still create a shared_ptr on
a raw pointer), making the `Manager` keep `shared_ptr` on the library
help us a lot here.
After switching to Xapian-based search in the library/catalog, an empty
query stopped acting as a match-all query. This commit restores the old
behaviour in that regard.
Catalog filtering should now be case/diacritics insensitive for all
fields. However it is not validated for language, name and category
fields, and is validated for tags, creator & publisher only for text
supplied in the filter (but not for values read from the book).
Catalog filtering by titles/description was sensitive to diacritics
present in the query string. Fixed that.
Also enhanced the unit test to validate the insensitivity to diacritics
present in either the title/description or the query string.
Now the LibraryTest.filterCheck unit-test validates the actual entries
returned by `Library::filter` (previously only the count of the results
was checked).
The new unit-test fails with a reason not expected before it was
written. The `Library::filter()` operation returns a correct result
after the call to `removeBookById()` (this was a surprise!) but it has
a side-effect of re-adding an empty book with the id still surviving
in the search DB (the emptiness of this re-created book doesn't allow
it to pass the other filtering criteria, which explains why the result
of `Library::filter()` is correct). Had to add a special check
to the new unit-test against that hidden side-effect of
`Library::removeBookById()` + `Library::filter()` combination.
As we use the main library of gtest (if already installed)
we don't need to (and must not) define a main function for the tests.
Does the same (use main library) if we use the subproject.