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