gix-blame: add test for file with two roots

gix-blame/tests/blame.rs

@@ -333,6 +333,37 @@ fn diff_disparity() {
     }
 }
 
+#[test]
+fn file_that_was_added_in_two_branches() -> gix_testtools::Result {
+    let worktree_path = gix_testtools::scripted_fixture_read_only("make_blame_two_roots_repo.sh")?;
+
+    let Fixture {
+        odb,
+        mut resource_cache,
+        suspect,
+    } = Fixture::for_worktree_path(worktree_path.to_path_buf())?;
+
+    let source_file_name = "file-with-two-roots.txt";
+    let lines_blamed = gix_blame::file(
+        &odb,
+        suspect,
+        None,
+        &mut resource_cache,
+        source_file_name.into(),
+        gix_blame::Options::default(),
+    )?
+    .entries;
+
+    assert_eq!(lines_blamed.len(), 4);
+
+    let git_dir = worktree_path.join(".git");
+    let baseline = Baseline::collect(git_dir.join("file-with-two-roots.baseline"), source_file_name.into())?;
+
+    pretty_assertions::assert_eq!(lines_blamed, baseline);
+
+    Ok(())
+}
+
 #[test]
 fn since() -> gix_testtools::Result {
     let Fixture {

gix-blame/tests/fixtures/make_blame_two_roots_repo.sh

@@ -0,0 +1,40 @@
+#!/usr/bin/env bash
+set -eu -o pipefail
+
+git init -q
+git config --local diff.algorithm histogram
+
+git config merge.ff false
+
+git checkout -q -b main
+
+seq 1 4 > unrelated-file.txt
+git add unrelated-file.txt
+git commit -q -m c1
+
+seq 1 4 > file-with-two-roots.txt
+git add file-with-two-roots.txt
+git commit -q -m c2
+
+seq 1 5 > file-with-two-roots.txt
+git add file-with-two-roots.txt
+git commit -q -m c3
+
+git checkout -b different-branch
+git reset --hard HEAD~2
+
+seq 4 6  > file-with-two-roots.txt
+git add file-with-two-roots.txt
+git commit -q -m c10
+
+seq 4 8 > file-with-two-roots.txt
+git add file-with-two-roots.txt
+git commit -q -m c11
+
+git checkout main
+git merge different-branch || true
+seq 1 8 > file-with-two-roots.txt
+git add file-with-two-roots.txt
+git commit -q -m c20
+
+git blame --porcelain file-with-two-roots.txt > .git/file-with-two-roots.baseline