chore: import upstream snapshot with attribution

tests/test_apply_diff_helpers.py

@@ -0,0 +1,74 @@
+"""Direct tests for the apply_diff helpers to exercise corner cases."""
+
+from __future__ import annotations
+
+import pytest
+
+from agents.apply_diff import (
+    Chunk,
+    ParserState,
+    _apply_chunks,
+    _find_context,
+    _find_context_core,
+    _is_done,
+    _normalize_diff_lines,
+    _read_section,
+    _read_str,
+)
+
+
+def test_normalize_diff_lines_drops_trailing_blank() -> None:
+    assert _normalize_diff_lines("a\nb\n") == ["a", "b"]
+
+
+def test_is_done_true_when_index_out_of_range() -> None:
+    state = ParserState(lines=["line"], index=1)
+    assert _is_done(state, [])
+
+
+def test_read_str_returns_empty_when_missing_prefix() -> None:
+    state = ParserState(lines=["value"], index=0)
+    assert _read_str(state, "nomatch") == ""
+    assert state.index == 0
+
+
+def test_read_section_returns_eof_flag() -> None:
+    result = _read_section(["*** End of File"], 0)
+    assert result.eof
+
+
+def test_read_section_raises_on_invalid_marker() -> None:
+    with pytest.raises(ValueError):
+        _read_section(["*** Bad Marker"], 0)
+
+
+def test_read_section_raises_when_empty_segment() -> None:
+    with pytest.raises(ValueError):
+        _read_section([], 0)
+
+
+def test_find_context_eof_fallbacks() -> None:
+    match = _find_context(["one"], ["missing"], start=0, eof=True)
+    assert match.new_index == -1
+    assert match.fuzz >= 10000
+
+
+def test_find_context_core_stripped_matches() -> None:
+    match = _find_context_core([" line "], ["line"], start=0)
+    assert match.new_index == 0
+    assert match.fuzz == 100
+
+
+def test_apply_chunks_rejects_bad_chunks() -> None:
+    with pytest.raises(ValueError):
+        _apply_chunks("abc", [Chunk(orig_index=10, del_lines=[], ins_lines=[])], newline="\n")
+
+    with pytest.raises(ValueError):
+        _apply_chunks(
+            "abc",
+            [
+                Chunk(orig_index=0, del_lines=["a"], ins_lines=[]),
+                Chunk(orig_index=0, del_lines=["b"], ins_lines=[]),
+            ],
+            newline="\n",
+        )