Add unit tests

[xoofx]

The generated API requires to check that the API is exposed correctly

Here is the list of API that needs to be tested with unit tests:

HELP much welcome

• annotated_commit.generated.cs
• apply.generated.cs
• attr.generated.cs
• blame.generated.cs
• blob.generated.cs
• branch.generated.cs
• buffer.generated.cs
• checkout.generated.cs
• cherrypick.generated.cs
• clone.generated.cs
• commit.generated.cs
• common.generated.cs
• config.generated.cs
• cppast.generated.cs
• deprecated.generated.cs
• describe.generated.cs
• diff.generated.cs
• errors.generated.cs
• filter.generated.cs
• global.generated.cs
• graph.generated.cs
• ignore.generated.cs
• index.generated.cs
• indexer.generated.cs
• libgit2.generated.cs
• mailmap.generated.cs
• merge.generated.cs
• message.generated.cs
• net.generated.cs
• notes.generated.cs
• object.generated.cs
• odb.generated.cs
• odb_backend.generated.cs
• oid.generated.cs
• oidarray.generated.cs
• pack.generated.cs
• patch.generated.cs
• pathspec.generated.cs
• proxy.generated.cs
• rebase.generated.cs
• refdb.generated.cs
• reflog.generated.cs
• refs.generated.cs
• refspec.generated.cs
• remote.generated.cs
• repository.generated.cs
• reset.generated.cs
• revert.generated.cs
• revparse.generated.cs
• revwalk.generated.cs
• signature.generated.cs
• stash.generated.cs
• status.generated.cs
• strarray.generated.cs
• submodule.generated.cs
• tag.generated.cs
• trace.generated.cs
• transaction.generated.cs
• transport.generated.cs
• tree.generated.cs
• types.generated.cs
• worktree.generated.cs