test: cover trailing-separator and dedup arcs in from_body inject

Close the last uncovered partial branch (empty segment / duplicate in
existing-comment merge loop) behind #1852 comment preservation.

Signed-off-by: Alex Chen <l46983284@gmail.com>

Author: alexchen-sys

tests/unit/test_regressions.py

@@ -2526,6 +2526,22 @@ def test_inject_from_body_comments_branches_issue_1852():
         "    ",
         comment_prefix="  #",
     ) == ("from foo import alpha  # disabled; nested")
+    # empty segment from a trailing ";" in an existing comment is skipped
+    assert _inject_from_body_comments(
+        "from foo import alpha  # nested;",
+        ["disabled"],
+        "\n",
+        "    ",
+        comment_prefix="  #",
+    ) == ("from foo import alpha  # disabled; nested")
+    # duplicate body text is not re-appended from the existing comment
+    assert _inject_from_body_comments(
+        "from foo import alpha  # nested",
+        ["nested", "disabled"],
+        "\n",
+        "    ",
+        comment_prefix="  #",
+    ) == ("from foo import alpha  # nested; disabled")
 
 
 def test_force_single_line_emits_plain_before_as_with_body_comment_issue_1852():