File fixtures.rs

backend/tests/git/fixtures.rs:None–None

use digraph::git::{
    Client, DataRoot, FetchTopicLiveSearch, FetchTopicLiveSearchResult, IndexMode, Mutation,
    OnMatchingSynonym, RepoLink, RepoTopic, Search, UpsertLink, UpsertLinkResult, UpsertTopic,
    UpsertTopicResult,